contents — r through s...68th annual meteoritical society meeting (2005) alpha_r-s.pdf refractory...

$: CONTENTS — R through S...68th Annual Meteoritical Society Meeting (2005) alpha_r-s.pdf Refractory Inclusions from the CM2 Chondrite LEW85311 S. B. Simon, C. G. Keaton, and L. Grossman$
CONTENTS — R through S

Sources of Basaltic Volcanism in the Arcadia Planitia, Mars M. L. Rampey, K. A Milam, H. Y. McSween Jr., J. E. Moersch, and P. R. Christensen......................... 5192

LAP 02 205: An Evolved Member of the Apollo 12 Olivine Basalt Suite? K. Rankenburg, A. Brandon, M. Norman, and K. Righter...................................................................... 5294

Constraining Models for the Production of Nuclides by Energetic Particles in Early Solar System Matter

R. C. Reedy ............................................................................................................................................. 5266

Using Light Lithophile Elements to Evaluate Crustal Assimilation on Mars V. S. Reynolds, J. G. Ryan, W. F. McDonough, and H. Y. McSween Jr. ................................................ 5118

The Contribution of Lunar Meteorites to Our Understanding of the Moon K. Righter ............................................................................................................................................... 5316

Australasian Tektites and Atomic Bomb Glass: Close Similarity in Their Shape Percentages M. C. L. Rocca........................................................................................................................................ 5001

Bajo Hondo, Chubut, Patagonia, Argentina: A New Meteorite Impact Crater in Basalt? M. C. L. Rocca........................................................................................................................................ 5002

La Criolla Meteorite Shower, Entre Rios, Argentina: Meteoroid’s Helicoentric Orbit M. C. L. Rocca........................................................................................................................................ 5003

The Araguainha Impact Structure, Central Brazil: A Perfect Example to Study Collapse of Large Complex Impact Craters

R. Romano, W. U. Reimold, and C. Lana ............................................................................................... 5248

Diamonds in Carbon Spherules — Evidence for a Cosmic Impact? W. Rösler, V. Hoffmann, B. Raeymaekers, D. Schryvers, and J. Popp................................................... 5114

An SEM-based Cathodoluminescence Study of Mesostasis in the Nakhlites Nakhla, Lafayette, and MIL03346

D. Rost and E. P. Vicenzi ....................................................................................................................... 5286

Structure and Texture of Organic Matter in CV and CO Carbonaceous Chondrites. Relationship to Metamorphic Process

J-N Rouzaud, L. Bonal, and E. Quirico.................................................................................................. 5199

Shock and Annealing in Ureilites A. E. Rubin ............................................................................................................................................. 5007

A New Aqueous Alteration Index for CM Carbonaceous Chondrites A. E. Rubin, J. M. Trigo-Rodriguez, and J. T. Wasson........................................................................... 5050

Al-26 in UOC Chondrules: Imprints of Thermal Metamorphism in a Nebular Environment N. G. Rudraswami, J. N. Goswami, and M. P. Deomurari .................................................................... 5071

A Terrestrial Fractionation Line for the Oxygen Isotopes of Phosphate Minerals and Its Application to Meteorites

D. Rumble III, C. M. Corrigan, R. E. Blake, and T. J. McCoy ............................................................... 5130

68th Annual Meteoritical Society Meeting (2005) alpha_r-s.pdf

Discrimination of Acapulcoites and Lodranites from Winonaites D. Rumble III, A. J. Irving, T. E. Bunch, J. H. Wittke, and S. M. Kuehner............................................. 5138

Geochemical Constraints for the Origin of the Steinbach (IVA) Stony Iron Meteorite A. Ruzicka and M. Hutson ...................................................................................................................... 5279

Widespread Aluminium-26-induced Meltdown of Planetesimals and an Emerging Rational Early Solar System Chronology

I. S. Sanders............................................................................................................................................ 5293

Cl-Amphibole in Melt Inclusion from MIL 03346: Evidence for Martian Soil Assimilation V. Sautter, A. Jambon, and O. Boudouma .............................................................................................. 5205

Chemical Evidence of Asteroidal Fragments (Iron Meteorites and/or Pallasites) in the Earth’s Upper Continental Crust?

G. Schmidt, H. Palme, and K.-L. Kratz .................................................................................................. 5015

Petrogenesis of Apollo 15 Olivine- and Quartz-Normative Mare Basalts D. W. Schnare, L. A. Taylor, J. M. D. Day, and M. D. Norman............................................................. 5214

Si in Metal of CR-Chondrites: Indicator for Incomplete Metal-Silicate Equilibration at High Cooling Rates

Th. W. Schoenbeck and H. Palme........................................................................................................... 5167

Palladium – Silver Systematics of the Early Solar System M. Schönbächler, R. W. Carlson, and E. H. Hauri ................................................................................ 5231

Characterizing a Model Sample for Desert Weathering Influence on Noble Gases in Martian Meteorites

S. P. Schwenzer, J. Huth, S. Herrmann, and U. Ott ............................................................................... 5027

Chondrite Evidence for Accretion of Impact Debris in the Protoplanetary Disk E. R. D. Scott and A. N. Krot.................................................................................................................. 5319

Lithium Isotope Compositions of Martian and Lunar Reservoirs H.-M. Seitz, G. P. Brey, S. Weyer, S. Durali, U. Ott, and C. Münker..................................................... 5102

The Probable Primitive H-Material in the Krymka Chondrite V. P. Semenenko and A. L. Girich .......................................................................................................... 5013

Exposure Histories of Three Meteorites from Rio Cuarto Argentina F. Serefiddin, G. F. Herzog, P. H. Schultz, and L. Schultz..................................................................... 5292

Melt-Vein Crystallization as an Alternative Means of Constraining Shock Pressures in Chondrites T. G. Sharp, Z. Xie, and P. S. De Carli .................................................................................................. 5290

Petrogenetic Linkages Between the Mg-Suite and Other Episodes of KREEP Basaltic Magmatism C. K. Shearer, L. E. Borg, and J. J. Papike ............................................................................................ 5243

Chemical Characteristics of Nakhlite, MIL 03346 N. Shirai and M. Ebihara ....................................................................................................................... 5245

Nondestructive 3D Structure and Morphology of Meteorites A. S. Simionovici, L. Lemelle, Ph. Gillet, B. Zanda, G. Libourel, and P. Bleuet .................................... 5132


Refractory Inclusions from the CM2 Chondrite LEW85311 S. B. Simon, C. G. Keaton, and L. Grossman ......................................................................................... 5122

Melting of Allende at Pressures Between 1 and 25 Mpa S. J. Singletary, T. L. Grove, and M. J. Drake ....................................................................................... 5258

Status of the James M. DuPont Meteorite Collection 1995 to 2004 P. P. Sipiera, K. J. Cole, J. R. Schwade, G. A. Jerman, and B. D. Dod ................................................. 5008

Moldavites from the Cheb Basin, Czech Republic R. Skála and M. Čada............................................................................................................................. 5055

Influence of Titanium Content on Crystal Structure of Iron Monosulfide R. Skála and M. Drábek ......................................................................................................................... 5057

Investigating Fine-grained Constituents of Meteorites Using FIB and SEM-STEM C. L. Smith and M. R. Lee ...................................................................................................................... 5166

Mineralogy of the Lunar Meteorites Kalahari 008 and Kalahari 009 A. K. Sokol and A. Bischoff .................................................................................................................... 5059

26Al-26Mg Chronology of the D’Orbigny and Sahara 99555 Angrites L. Spivak-Birndorf, M. Wadhwa, and P. E. Janney................................................................................ 5097

Shock-generated Melt Networks in Anorthositic Target Rocks from the Manicouagan Impact Structure

J. G. Spray and E. L. Walton.................................................................................................................. 5077

Auger Spectroscopy as a Complement to NanoSIMS Studies of Presolar Materials F. J. Stadermann, C. Floss, E. Zinner, A. Nguyen, and A. S. Lea .......................................................... 5123

TOF-SIMS, NanoSIMS, and TEM Analysis of Anhydrous Cluster IDPs T. Stephan, P. Hoppe, and I. Weber ....................................................................................................... 5157

Shock Recovery Experiments Confirm the Possibility of Transferring Viable Microorganisms from Mars to Earth

D. Stöffler, C. Meyer, J. Fritz, G. Horneck, R. Möller, C. S. Cockell, J. P. de Vera, and U. Hornemann .......................................................................................................... 5048

The Origin of Impactors During the Inner Solar System Cataclysm R. G. Strom, R. Malhotra, T. Ito, F. Yoshida, and D. A. Kring .............................................................. 5070

Microstrcutre of a Presolar Hibonite Grain R. M. Stroud, L. R. Nittler, C. M. O’D. Alexander, F. J. Stadermann, and E. K. Zinner ....................... 5171

60Fe-60Ni Systematics of Some Achondrites N. Sugiura and Q.-Z. Yin ........................................................................................................................ 5061

Recent Progress in the Modeling of Core-Collapse Supernovae F. D. Swesty............................................................................................................................................ 5341

Petrological and Ar-Ar Studies of Shocked Chondrites T. D. Swindle, D. A. Kring, J. Bond, E. Olson, and C. Jones ................................................................. 5295

Lunar Impact Histories Deduced from Ar-Ar T. D. Swindle, D. A. Kring, B. A. Cohen, J. W. Delano, and N. E. B. Zellner........................................ 5116


SOURCES OF BASALTIC VOLCANISM IN THE ARCADIA PLANITIA, MARS. M. L. Rampey1, K. A. Mi-lam1, H. Y. McSween, Jr. 1, J. E. Moersch1 and P. R. Christensen2

1Department of Earth and Planetary Sciences, University of Ten-nessee, Knoxville, Tennessee 37996-1410, [email protected], 2Department of Geological Sciences, Arizona State University, Tempe, Arizona

Introduction: The surface of Mars is considered to consist

largely of volcanic materials of basaltic and andesitic composi-tions, referred to a surface type 1 (ST1) and surface type 2 (ST2) [1,2]. These were shown to be dominant in spatially distinct re-gions, effectively making separate hemispheres of each. The manner in which entire hemispheres of distinct compositions could be formed, however, remains unexplained. Others have suggested that the ST2 material is not true andesite lava but weathered ST1 (basalt) [3].

We examined surface compositions of an anomalously ST1-rich area of the Mars northern hemisphere, in order to discover the source of the ST1 materials. Our intention was to contribute to the ongoing debate about the nature of the relationship be-tween ST1 and ST2. We refer to the study area as the Tyndall Dome Field (TDF - informal name not formally accepted by the International Astronomical Union), located in the western Arca-dia Planitia region. This large area (~ 1.8 x 106 km2) contains hundreds of small (diameters <10 km) lava domes, enigmatic lineaments, lava flows and impact craters, all superposed upon a broad, low-relief plain. The present work focuses on the domes. We used Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS) thermal IR data to closely analyze surface compositions.

Results: We found that the domes are more ST1-rich than are the plains. The proportion of ST1 found in the plains material decreases markedly with distance from domes. THEMIS data show that the domes are shedding material onto the plains.

Conclusions: We conclude that the TDF domes are point-sources (vents) for ST1 lava production in this sector of the Mars northern hemisphere. The domes appear to have created aureoles of relatively ST1-rich deposits on the ST2-rich plains materials.

Implications: This work cannot resolve the debate about the identity of ST2, however, the weathered basalt hypothesis is sup-ported by the observations that the only vents producing lava that have been found in the TDF produced basalt; additionally, the domes are relatively young, local topographic highs and there-fore could logically have escaped weathering by standing above the plains weathering agent (an ancient ocean?) or by being of later date than the weathering event(s). It remains possible, how-ever, that andesite lava plains might have been extruded onto the TDF surface and later, basaltic volcanism produced the domes.

References: [1] Bandfield J. et al. 2000, Science, 287, 1626-1630. [2] Hamilton V.E. et al. 2001, Journal of Geophysical Re-search, 106, 14,733-14,746. [3] Wyatt M. B. and McSween Jr. H. Y. 2002, Nature, 417, 263-266.

68th Annual Meteoritical Society Meeting (2005) 5192.pdf

mailto:[email protected]

LAP 02 205: AN EVOLVED MEMBER OF THE APOLLO 12 OLIVINE BASALT SUITE? K. Rankenburg1, A. Brandon1, M. Norman2 and K. Righter1. 1NASA/JSC, Mailcode KR, Hous-ton, TX 77058. E-mail: [email protected]. 2 Re-search School of Earth Sciences, Australian National University, Canberra ACT 0200.

Introduction: LAP02205 is a low-Ti mare-basalt meteorite

which was discovered in the LaPaz Ice Field in Antarctica [1]. The petrology and geochemistry of LAP02205 indicates that this meteorite is unique among lunar samples in its evolved magmatic nature (e.g. low Mg# of 0.33, high concentrations of incompati-ble elements). Previous work [2-8] suggests that LAP02205 is a younger variant of volcanism that produced the Apollo 12 pi-geonite, ilmenite, or olivine basalts [2,5-7]. This hypothesis is addressed here on the basis of combined major and trace element modeling and isotope systematics.

Results: The major element, trace element and Rb-Sr iso-topic compositions were measured for hand-picked pyroxene, ilmenite, plagioclase and shock melt glass by EMP and LA-ICP-MS. The glass composition compares very well with published bulk rock compositions of LAP02205 [2-4,8] and is therefore used to model parental melt compositions. Measured trace ele-ment concentrations of glass, clinopyroxene and plagioclase are consistent with equilibrium partitioning between these phases [D’s taken from ref. 9]. The Rb-Sr data on leached mineral frac-tions of LAP02205 define a nine point isochron of 2956±14 Ma with an initial 87Sr/86Sr of 0.699840±11, MSWD=0.43). The whole rock leachate plots only slightly outside the 2σ-error inter-val, consistent with only minimal terrestrial contamination in the Antarctic environment. This crystallization age is consistent with previous results [7].

Discussion: The major and trace element composition of LAP02205 is consistent with a derivation from primitive Apollo 12 olivine basalts by fractional crystallization. Thermodynamic modeling demonstrates that the fractionating phases are mainly olivine with minor amounts of pigeonite. Ratios of incompatible trace elements therefore should be similar in LAP02205 and its parental magma. Assuming a parental melt similar to average Apollo 12 basalts, crustal contamination of LAP02205 can be excluded based on Sr/Sm and Eu/Sm ratios, which are high in lunar feldspathic crust [10]. However, slightly altered Ti/Sm, Ti/Y and Sc/Y ratios allow for assimilation of 6-7% of KREEPy material [av. from ref. 11]. Available data for Apollo 12 basalts suggest a lower source 87Rb/86Sr ratio compared to the LAP02205 source region [7]. However, this discrepancy might be resolved by assimilation of high Rb/Sr KREEP at 2.96 Ga. Recycling of KREEP into the moon’s interior might be important for younger lunar magmatism in that it provides a suitable heat source for the generation of these magmas. References: [1] McCoy T. et al. (2003) Antarctic Meteorite Newsletter 26 (2). [2] Joy K.H. et al. (2004) LPS 35, Abstract #1545. [3] Anand M. et al. (2004) LPS 35, Abstract #1626. [4] Joliff B.L. et al. (2004) LPS 35, Abstract #1438. [5] Day M.D. (2005) LPS 36, Abstract #1419. [6] Collins S.J. (2005) LPS 36, Abstract #1141. [7] Nyquist L.E. et al. (2005) LPS 36, Abstract #1374. [8] Joy K.H. et al. (2005) LPS 36, Abstract #1697, #1701. [9] Snyder G.A. et al. (1992) Geochim. et Cosmochim. Acta 56, 3809-3823. [10] Korotev L.K. et al. (2003) Geochim. et Cosmo-chim. Acta 67, 4895-4923. [11] Norman M.D. et al. (2002) Earth and Planet. Sci. Lett. 202, 217-228.


CONSTRAINING MODELS FOR THE PRODUCTION OF NUCLIDES BY ENERGETIC PARTICLES IN EARLY SOLAR SYSTEM MATTER. R. C. Reedy1 1Institute of Me-teoritics, Univ. of New Mexico, Albuquerque, NM 87131 USA. E-mail: rreedy @unm.edu

Introduction: Irradiations by energetic particles have often

been proposed to explain isotopic anomalies in solar system mat-ter, including some in the very early solar system. There is good evidence that short-lived radionuclides like 0.7 Myr Al-26 and 1.5 Myr Be-10 were live in the early solar system. Some argue that these radionuclides were made by a local irradiation [e.g., 1,2], while others [e.g., 3,4] argue against local irradiations pro-ducing most anomalies and for nucleosynthetic processes being the source of many isotopic anomalies.

It has been proposed that some radionuclides were made by the galactic cosmic rays (GCR) or other interactions in interstel-lar space before the solar system’s formation. Densch et al. [5] argued that the Be-10 incorporated in CAIs was made by GCRs in interstellar space. Modern observations and calculations can be used to help constrain models for early local irradiations.

Modern Observations: Live Al-26 in the galaxy has been often observed [6]. Be-7 and Be-10 make up 52% and 4%, re-spectively, of the Be nuclei in modern GCRs [7]. The fluxes of He-3 in modern solar energetic particles (SEPs) are very low [8].

Nature of the Ancient Particles: There is very little known about the energetic particles in and near the early solar system. Modern observations, such as given above, can give us clues to the compositions of the GCR and SEP (mainly protons and some He-4) and to their spectral shapes (energy power laws) but do not provide any guidance to their fluxes. Both types of energetic particles probably had higher fluxes than today.

Production Calculations: Models depend on the specific scenario, such as what is being irradiated where and whether the system was opened or closed to other matter. Many irradiation models need to be examined with the latest cross sections.

Such models should also be used to calculate all other iso-topic anomalies that would be made by such irradiations. To make the amounts of Al-26 observed in CAIs requires large amounts to be produced, as stable Al-27 is very abundant. Such a high fluence of particles would make many other isotopic ef-fects. For example, there should be much C-13 and N-15 made from O, or Cr from Fe. If the amount of stable Be-9 is very low but the amounts of the target elements for making Be-10 (C or O) are high, only a low particle fluence is needed and other isotopic effects would be negligible. Because of the lack of many iso-topic anomalies, scenarios with only limited production by local irradiations (e.g., Be-10) and much production by stars (e.g. Al-26 and Ca-41) [e.g., 3,4] are most plausible.

Acknowledgments: This work supported by NASA’s CCP. References: [1] Leya I. et al. 2003. Astrophys. J. 594: 605-

616. [2] Gounelle M. et al. 2001. Astrophys. J. 548: 1051-1070. [3] Marhas K. K. and Goswami J. N. 2004. New Astron. Rev. 48: 139-144. [4] MacPherson, G. J. et al. 2003. Geochim. Cosmo-chim. Acta 67: 3165-3179. [5] Desch S. J. et al. 2004. Astrophys. J. 602: 528-542. [6] Diehl R. et al. 2004. New Astron. Rev. 48: 81-86. [7] Lukasiak A. et al. 1994. Astrophys. J. 423: 426-431. [8] Ho G. C. et al. 2005. Astrophys. J. 621: L141-L144.


USING LIGHT LITHOPHILE ELEMENTS TO EVALUATE CRUSTAL ASSIMILATION ON MARS. V. S. Reynolds1, J. G. Ryan2, W. F. McDonough3, and H. Y. McSween, Jr.1. 1Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, USA. [email protected] 2Department of Geology, University of South Florida, Tampa, FL 33620, USA, 3Geochemistry Labora-tory, Department of Geology, University of Maryland, College Park, MD 20742, USA

Introduction: Systematic variations in rare earth element

partitioning, oxidation state, and Nd and Sr isotopic ratios sug-gest basaltic shergottites represent either various degrees of crustal assimilation or sample a heterogeneous mantle [1-5]. The apparently oxidized nature of the enriched (i.e. “crust-like”) component could indicate interaction with an ancient ocean or other long-lived water source on Mars. On Earth, low-temperature hydrothermal alteration of oceanic crust results in elevated concentrations of B and Li, and high δ7Li and δ11B while Be contents are unaffected [6, 7]. As altered crust is sub-ducted, dewatering reactions transport fluid-mobile B and Li from the slab, but leave Be relatively unchanged. The different partitioning behaviors of these light lithophile elements provide a means to track the presence of altered oceanic crust or fluids de-rived from altered oceanic crust in the source regions of subduc-tion-related lavas. Using a single detector inductively coupled plasma mass spectrometer (ICP-MS) at the University of Mary-land, we analyzed whole-rock Li and Be concentrations in six Martian meteorites (Shergotty, Zagami, Los Angeles, EETA 79001, Dhofar 019, and Chassigny) to evaluate whether the “crust-like” component in the basaltic shergottites experienced low-temperature hydrothermal alteration.

Results: A positive correlation between Li and Be in most meteorites suggests these elements behave incompatibly and pre-serve igneous conditions. Dhofar 019 has an unusually high Li content, possibly due to terrestrial weathering. When compared to ε143Nd, Li and Be in Zagami, Shergotty, Los Angeles, and EETA 79001 display similar trends as ε143Nd vs. La/Yb, fO2, and 87Sr/86Sr, suggesting the “crust-like” component is enriched in these elements. Li and Be values for Chassigny plot opposite the oxidized meteorites, apparently representing mantle Li and Be compositions. A strong correlation is not observed between Li or Be and δ18O [8], suggesting the “crust-like” component was not altered at low temperatures. Whole rock Li data contrast with in situ pyroxene data by [9, 10] who concluded lower Li and B con-tents in pyroxene rims vs. cores suggests Li and B were lost dur-ing magma degassing.

References: [1] Herd C.D.K. et al. (2002) Geochimica Cos-mochimica Acta 66, 2025-2036. [2] Jones J.H. (1989) Proceed-ings Lunar Planetary Science IXX, 465-474. [3] Longhi J. (1991) Proceedings Lunar Planetary Science XXI, 695-709. [4] Wad-hwa M. (2001) Science 291, 1527-1530. [5] Borg L.E. (2002) Workshop on Unmixing the SNCs #6004. [6] Seyfried et al. (1983) Geochimica Cosmochimica Acta 48, 557-569. [7] Brenan et al. (1998) Geochimica Cosmochimica Acta 62, 3337-3347. [8] Franchi I.A. et al. (1999) Meteoritics & Planetary Science, 34, 657-661. [9] Lentz R.C.F. et al. (2001) Geochimica Cosmo-chimica Acta 65, 4551-4565. [10] Herd C.D.K. et al. (2005) Geo-chimica Cosmochimica Acta 69, 2431-2440.


THE CONTRIBUTION OF LUNAR METEORITES TO OUR UNDERSTANDING OF THE MOON. K. Righter1. 1Mailcode KT, NASA Johnson Space Center, 2101 NASA Park-way, Houston, TX 77058; [email protected]

Introduction: The discovery of a meteorite from the Moon

in 1982 sparked interest in samples from regions on the Moon that were not sampled by the Apollo or Luna missions. Cur-rently, there are 37 recognized lunar meteorites in world collec-tions, comprising 26.4 kg, and representing many unique sites on the Moon [1] (some of the 37 are launch paired).

Apollo-era paradigms: Intensive study of the Apollo and Luna sample collections has created a detailed history of the Moon with several specific highlights [2]: development of an early feldspathic crust that floated on a lunar magma ocean (LMO), basaltic magmatism that lasted from 4.4 to 2.7 Ga, bi-modal high and low Ti volcanism, an incompatible element en-riched residual liquid from crystallization of the LMO (KREEP), and a spike in the impact flux at 3.9 Ga.

Lunar meteorites as a test of the paradigms: Lunar mete-orites have provided a wealth of new information, requiring revi-sion to some specific scenarios arising out of studies of the Apollo sample collection. Studies of feldspathic lunar meteorites have revealed a rich compositional and petrologic diversity that is inconsistent with a simple picture of a flotation crust of ferroan anorthosite [3]. On the other hand feldspathic clasts from high-lands breccias yield Sr and Nd isochrons of 4.4 Ga, providing evidence for an ancient LMO [4]. Evolved and young low Ti basalts provide evidence that the Moon maintained widespread active magmatism up to ~2.9 Ga [5,6]. Impact melt clasts from meteoritic breccias have yielded ages that do not confirm or dis-prove the lunar cataclysm hypothesis, pushing the resolution of this controversial topic to future sample return missions [7]. New high-resolution dating techniques have led to impact ages different from the cataclysmic spike at 3.85 Ga [8]. The idea that KREEP existing only in the early Moon (3.8 to 4.6 Ga) has been challenged by evidence from a new lunar gabbro with a 2.9 Ga age and KREEP connections [9].

Conclusions and future: Lunar meteorites have provided the opportunity to test models for the origin and evolution of the Moon, which were based largely on Apollo samples. In a few cases, models have survived intact, but in most cases, new data from meteorites have required revision. The random sampling of the surface represented in the meteorite collection has great po-tential in making the connection between sample suites and global lunar imaging efforts, and studies of terranes [10,11].

References [1] http://epsc.wustl.edu/admin/resources/moon_meteorites.html [2] Taylor S. R. 1982. Planetary Science: A Lunar Perspective. LPI, Houston, TX 335 pp. [3] Korotev, R. et al. 2003. Geo-chimica Cosmochimica Act 67, 4895-4923. [4] Nyquist, L. et al. 2002. Lunar Planetary Science XXXIII, #1289. [5] Fagan, T. et al. 2002. Meteoritics Planetary Science 37, 371-394. [6] Nyquist, L. et al., 2005. Lunar Planetary Science XXXVI, #1374. [7] Cohen, B. et al. (2000) Science 290, 1754-1756. [8] Gnos, E. et al. 2004. Science 305: 657-659. [9] Borg, L.E. et al. 2004. Nature 432, 209-211. [10] Hill, D.H. and Boynton, W.V. 2003. Meteoritics Planetary Science 38, 595-626. [11] Warren, P. 2004. Lunar Planetary Science XXXV, # 1718.


http://epsc.wustl.edu/admin/resources/moon_meteorites.html

AUSTRALASIAN TEKTITES AND ATOMIC BOMB GLASS: CLOSE SIMILARITY IN THEIR SHAPE PERCENTAGES. M. C. L. Rocca , Mendoza 2779-16A, Ciudad de Buenos Aires, Argentina, (1428DKU), [email protected].

Introduction: Tektites are small greenish to jet black glass bodies found in large but limited areas, or strewn fields, on the sur-face of Earth. So far, tektites occur in 4 different strewn fields: North America ( Age : 35 Ma ), Europe ( 15 Ma ), Ivory Coast ( 1.1 Ma ) and Australasia ( 0.8 Ma ).

Tektites are subdivided in 4 groups: 1) normal or splash-form (showing sizes from half a centimeter up to 25 cm.), 2) aerodynami-cally shaped , 3) layered or Muong Nong (irregular chunks of glass up to 28 kilograms in weight) and 4) microtektites (always smaller than a few millimeters).

Splash-form tektites are best known from the Australasian strewn field and they come in a wide variety of different forms: spheres, ellipsoids, droplets, teardrops, dumbbells, etc. The largest known splash-form tektite is a 1.07 Kg. sphere found in Coco Grove, Luzon, Philippines.

Tektites are most probably distant ejecta produced in meteorite impact events. In this hypothesis, tektites are formed by melt splashed by impacts and their size and shape are controlled by sur-face tension as bodies in rotation. The shapes of splash-form tektites result from the solidification of rotating liquids in the upper terres-trial atmosphere.

Glass produced in atomic bomb tests shares most of the charac-teristics of tektites, e.g.: color and transparency, shapes, petro-graphies (e.g.: quartz , lechatelierite and cristobalite inclusions), Ferrous to Ferric Iron ratios and a very low water content.

Here I present numbers showing close similarity between the published percentages of their forms.

Reported australasian splash-form tektites shape percentages are the following: Spheres 70-60%, Ellipsoids 25%, Dumbbells 8% and Teardrops 4%. [1].

Published microtektite shape percentages from 2 cores col-lected from the South China Sea are the following:

Core MD 972142: Spheres 66%, Flat ellipsoids 7%, Strongly elongated 5% , Droplets 17% and Irregular forms 11%.

Core MD 972143: Spheres 62%, Flat ellipsoids 9%, Strongly elongated 7%, Droplets 10% and Irregular forms 17%.[2]

These numbers are very close to the shape percentages reported from atomic bomb glass produced in a Yucca Flat, Nevada, test:

Spheres 60%, Elongated forms, including teardrops 16%, Ir-regular forms 24%.[3]

More than half of the bodies ejected in both processes are spheres.

Most probably, this similarity in their shape’s percentage num-bers is related to the similarities in the launch and solidification mechanisms: e.g.: Tektite launch mechanism seems to be entrain-ment in impact-produced plumes of gas, similar in structure to the plumes produced by the tests of thermonuclear weapons.

Acknowledgements: This work was funded by The Planetary Society, Pasadena, CA, USA.

References: [1] McNamara K. and Bevan A. (2001) Tektites, booklet published by the Western Australian Museum, Perth, pp. 1-38. [2] Lee M-Y and Wei K-Y (2000) Meteoritics & Planetary Sci-ence 35: pp. 1151-1155. [3] Glass B.P. et al. (1987) Second Interna-tional Conference on Natural Glasses, Prague: pp. 361-369.



BAJO HONDO, CHUBUT, PATAGONIA, ARGENTINA: A NEW METEORITE IMPACT CRATER IN BASALT? M. C. L. Rocca , Mendoza 2779-16A, Ciudad de Buenos Aires, Argentina, (1428DKU), [email protected].

Introduction: Bajo Hondo is a very puzzling crater in Chubut Province, Patagonia, Argentina, ( S 42º15’ W 67º 55’).Diameter: 4.8 kilometers. This crater is in fact very similar to Barringer’s cra-ter, USA, but of a much more gigantic size. Bajo Hondo has a 100 to 150 meters raised rim. In the aerial photos there are also visible some 50-60 meters wide boulders resting on the crater’s rim. Bajo Hondo is located in the Somuncura plateau, 10 km. SE to the Sierra deTalagapa stratovolcano. The Sierra de Talagapa, which is part of the Somuncura plateau, consists of a large 25 x 10 kilometer strato-volcano.The large Talagapa volcanic center was active during late Oligocene-Miocene times erupting both pyroclastic ignimbritic flows and basaltic lava flows [1]. Bajo Hondo has been interpreted as a collapsed basaltic caldera [1,2]. Close examination of satellite images (LANDSAT, X-SAR ), aerial photographs, its published geologic map and a review of the geological characteristics of Bajo Hondo reveals flaws in the volcanic caldera interpretation. The lava in the surrounding plateaux was no doubt erupted from Sierra de Talagapa volcano during the Oligocene-Miocene.The crater is lo-cated on those older lava floods.The association of some lava floods to Bajo Hondo is quite doubtful. Probably the reported ones[2] were erupted by Sierra de Talagapa and not by Bajo Hondo itself. A re-ported “pyroclastic cone” located in the inner Western rim of Bajo Hondo [2] was probably erupted by Talagapa and now it is just an eroded and collapsed part of Bajo Hondo’s rim. There is also good evidence of uplifted strata exposed in the inner rims of Bajo Hondo. Uplifted Talagapa’s basaltic rock strata were probably misinter-preted as “vertical or almost vertical basaltic dykes located in the inner rims of Bajo Hondo” by the volcanologists [2]. Rocks ex-posed on Bajo Hondo’s rims are clearly pyroclastic:1) Lapilly–like basaltic breccia enclosing irregular clasts and blocks up to 3 meters in diameter. 2) A great abundance of 13 to 7 centimeter wide brown-redish scoriaceous bombs showing aerodynamic shapes and defor-mation. The peculiar shape of those glass bomb bodies prove that whilst still in a viscous state they must have flown through the air i.e. were ballisticaly transported. The same type of rocks are present in Lonar Lake’s crater rim, a well confirmed impact crater in basalt in India [3].

Bajo Hondo could be a gigantic maar [4]. Comparing aerial photos of both Bajo Hondo and several maars shows that they are very different both in their shape and rim’s characteristics. The hypothesis of Bajo Hondo as a maar can not be completelly rejected at the present stage of investigation but so far it seems to be quite unlikely. Bajo Hondo is probably too big to be a Maar.

If Bajo Hondo is in fact a maar then it would be the largest maar in the World. The author believes Bajo Hondo is in fact a mis-interpreted gigantic simple-type impact crater located on a volcanic plateau. Lonar Lake impact crater was misinterpreted as a volcanic caldera for many decades [3 ].The age of Bajo Hondo crater is esti-mated in less than 10 Ma. Further investigation of this interesting crater is in progress.


References: [1] Ardolino A. (1987) Direccion Nacional de Mineria y Geología Boletín 203:1- 91 in Spanish [2]Ardolino A. and Delpino D. (1986) Revista Asociacion Geologica Argentina 41:386-396 In Spanish [3]Fredriksson K. et al. (1973) Science 180: 862-864.[4]Ollier C.D. (1967)Bulletin Volcanologique 31, BV: 45-75.



LA CRIOLLA METEORITE SHOWER, ENTRE RIOS, ARGENTINA: METEOROID’S HELIOCENTRIC ORBIT. M. C. L. Rocca , Mendoza 2779-16A, Ciudad de Buenos Aires, Argentina, (1428DKU), [email protected].

Introduction: Asteroids and meteoroids in Earth crossing or-bits are classified depending on their heliocentric orbits in 2 groups: Apollos and Atens.

Apollos have Mean Distances to the Sun greater than 1.0 As-tronomical Unit ( 1 A.U. = 149,600,000 Km ) and Perihelion dis-tances smaller than 1.017 A.U..

Atens have Mean Distances smaller than 1.0 A.U. and Aphe-lion distances greater than 0.983 A.U..

When they are located at 1.0 A.U. of the Sun, meteoroids in Apollo-type Earth crossing orbits have heliocentric velocities always greater than Earth’s orbital velocity ( 29.9 Km/sec. ).Asteroid frag-ments encounter Earth at different speeds depending upon their di-rection of travel with respect to Earth, that is, either a prograde or retrograde direction of motion with respect to Earth’s counterclock-wise direction of orbital motion around the Sun.

Depending upon the direction they are traveling meteoroid’s geocentric velocities can vary enormously.

If the fragments are traveling in the same direction of the Earth’s motion then they must catch up our planet to enter into the atmosphere and make an impact. Thus their heliocentric velocities must be greater than Earth’s 29.9 Km/sec. when at 1.0 A.U. of the Sun.

This occurs mainly at any time between noon and midnight and specially at 6.00 hours p.m. every day.

La Criolla L5 Ordinary Chondrite meteorite shower fell on Jan. 6, 1985 at 18.15 Hs local at Estacion La Criolla , Entre Rios Prov-ince, Argentina ( S 31º 14’, W 58º 10’). Many thousands of meteor-ite specimens survived the fireball and hit the ground in a dispersion ellipse of 10 x 7 Km. Total mass recovered was about 50 Kg.

The author has performed a model of this event. Original meteoroid’s pre-atmospheric total mass was about 1

Ton. and it was orbiting the Sun in a prograde orbit. Earth passed Perihelion on January 3, 1985. In the case of La Criolla both the date and the hour of its fall

are exactly those ones that the meteoroid encounters Earth when our planet velocity’s vector is pointing towards the opposite direction.

So the La Criolla meteoroid encountered Earth exactly in the opposite direction of a head on collision ( it was a ‘rear collision’) and must have caught up it to enter into the atmosphere.

As consequence, the heliocentric orbital velocity of the La Criolla meteoroid must have been greater than 29.9 km/sec. at that date and orbital position ( about 0.98 A.U. of the Sun ).

No Aten-type heliocentric orbit can full match this velocity data in any way.

So, it must be concluded that the heliocentric orbit of the La Criolla meteoroid was of the Apollo-type.

Thus, La Criolla’s meteorites are in fact fragments of an Apollo-type asteroid.


Thanks to Dr. Daniel Acevedo ( CADIC, CONICET, Ushuaia city ) for his valuable help and comments about La Criolla’s meteor-ite fall characteristics and for his friendship.



THE ARAGUAINHA IMPACT STRUCTURE, CENTRAL BRAZIL: A PERFECT EXAMPLE TO STUDY COLLAPSE OF LARGE COMPLEX IMPACT CRATERS. R. Romano1, W. U. Reimold2 and C. Lana3. 1Dept. of Geology, UFOP, Brazil. [email protected]. 2 ICRG, School of Geosciences, Univ. of the Witwatersrand, Johannesburg, SA. 3Dept. of Earth Science and Eng., Imperial College London, UK.

Introduction: The 40-km-wide Araguainha impact crater

(16º49’S/52º59’W) is the largest and one of the best exposed complex crater in South America. This crater was excavated in horizontally lying sediments of the Parana Basin, Central Brazil, at approximately 245 Ma ago [1]. The target rocks comprise sequences of Permian to Devonian sediments and underlying crystalline basement rocks of Precambrian to Ordovician age [2]. This study presents results of structural observations along the main gravel road and along the Araguaia River. Both, the gravel road and the Araguaia River, crosscut the entire structure from NE to SW.

Structural Features: The outer 5 km of the Araguainha structure, including its crater rim, is characterized by radial and concentric normal fault zones. These faults bound several kilometer-scale blocks of the Upper Permian sediments (the Passa Dois Group). Bedding orientations of these sediments are generally (sub)horizontal. On a local scale, however, the bedding orientation is significantly steep. Folds in the outer 5 km of the structure are restricted to the upper 200 meters of sedimentary strata (the Passa Dois Group). These folds are strongly asymmetric, with NW-SE trending hinges. In contrast, the lower sedimentary strata (Tubarao Group) were not folded and remained relatively undeformed in the outer 5 km of the crater. Bedding orientation may change from horizontal to gently folded, with fold planes trending toward the center.

The annular trough is characterized by large scale folds. Two types of folding were observed: one dipping inward and outward with axes around NW-SE, and a second type of radial folding with fold axes around NE-SW. We interpret the geometry of these folds as a result of lateral constriction of the sediments during the inward horizontal movement.

In the central uplift, sandstones of the Tubarao Group show steep inward and outward dipping bedding orientations. The Devonian shales and siltstones of the Parana Group are intensely folded (kinked), with dips ranging from N to S and from E to W, respectively. The geometry of these folds suggests a horizontal component of movement that might have been parallel to the main inward/outward (centrifugal) compression, accompanied by lateral constriction of the strata.

Conclusions: Structural features observed at the present level of erosion at Araguainha are all consistent with the inward movement of the target rocks during gravity-driven cavity collapse of its transient cavity. Folding intensity increases toward the center. The geometry of these folds is in agreement with inward and upward movement of the target rocks and they reflect processes that were achieved by a substantial amount of horizontal constriction of the target rocks.

References: [1] Harmmerschmidt K. and Engelhardt W., 1995. Meteoritics 30:277-233. [2] Engelhardt W., Matthai S., and Walzebuck, J., 1992. Meteoritics and Planetary Sciences 27:442-457.


DIAMONDS IN CARBON SPHERULES — EVIDENCE FOR A COSMIC IMPACT? W. Rösler1, V. Hoffmann1, B. Raeymaekers2, D. Schryvers3, and J. Popp4. 1Institute of Geo-science, University of Tübingen, Sigwartstr. 10, D-72076 Tübin-gen, Germany. [email protected]. 2Infraserv Gendorf, D-84504 Burgkirchen, Germany. 3EMAT University of Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium. 4Institute of Physical Chemistry, University of Jena, Helmholtzweg 4, D-07743 Jena, Germany.

Introduction: On Earth, elemental carbon is produced as re-sult of a variety of biogenic or pyrogenic processes, usually lead-ing to graphitic forms of carbon. Extraterrestrial C may survive atmospheric entry [1-2] and the occurrence of high pressure/high temperature polymorphs, such as diamonds or fullerene-like forms of C may be indicative for impact events [3-5]. Here we report the finding of a new type of spherule-shaped, mm-sized, carbonaceous particles in soils, wide-spread over Europe, with stunning microscopic features and amazing physical properties.

Analytical methods: The particles were characterized using optical and electron microscopy techniques, such as SEM/EDX, TEM, HRTEM, SAED, and EELS. Raman, Infrared, and XRD spectra were obtained, magnetic and electric properties were studied using various techniques.

Preliminary results: Optical microscopy and SEM/EDX re-veal mainly cenospheres exhibiting foam-, sponge-, or cell-like internal structures with cell sizes of a few micron. Elemental compositions show a high portion of C but also considerable amounts of O. The matrix of the spherules consists of amorphous carbon, with nanometer-sized monocrystalline or polycrystalline diamonds embedded. In one specimen, micrometer-sized, flake-shaped diamonds could be identified inside the cell-like struc-tures. Raman data indicate fullerene-like structures in most spec-tra whereas the sharp diamond band could be identified in only one spectrum. The particles exhibit a wide range of magnetic properties, from diamagnetic to ferromagnetic; all are poor elec-tric conductors with strongly dielectric behavior.

This type of particles is not known from anthropogenic or biogenic sources, the physical properties resemble those of novel technogenic carbon materials. The occurrence is independent from geology and points to a regional high energy process which is necessary for formation of the observed diamond phases. Moreover, the first find of such particles was made in context with small scale crater-like structures with thermally severely altered rocks [6].

Hypothesis: We favor an impact related origin of the parti-cles with a cosmic carbon source. Formation of the carbon spher-ules from impactor material by ablation and vapor re-condensation or by formation of elemental C through the Boudu-ard reaction in the shock front of a bolide are possible. If our pre-liminary results can be confirmed, they may be the first observa-tion of significant carbon delivery to Earth with far reaching im-plications on many fields of science.

References: [1] D. E. Brownlee et al. 2002, Abstract #1786. 33th Lunar & Planetary Science Conference. [2] M. Kress et al. 2002. Meteoritics &Planetary Science 37:A82. [3] B. M. French 1998. Traces of Catastrophe LPI Contribution No. 954. pp. 102-103. [4] V. L. Masaitis 1998. Meteoritics &Planetary Science 33: 349-359. [5] P. R. Buseck 2002. Earth & Planetary Science Let-ters 203:781-792. [6] V. Hoffmann et al. 2005. This issue.



AN SEM-BASED CATHODOLUMINESCENCE STUDY OF MESOSTASIS IN THE NAKHLITES NAKHLA, LAFAYETTE, AND MIL03346. D. Rost and E. P. Vicenzi. Smithsonian Institution, Department of Mineral Sciences, Wash-ington, D.C. 20560, USA. E-mail: [email protected].

Introduction: Nakhlites contain secondary minerals com-

monly interpreted as resulting from preterrestrial alteration proc-esses [1] and/or caused by an evaporation event [2]. Late crystal-lizing minerals in the mesostasis (e.g. feldspars) with their high surface/volume, should be especially susceptible to alteration processes. Poorly crystalline phases that comprise “iddingsite” can be seen as reddish-brown stains associated with the mesosta-sis. These areas mark incipient alteration relative to the better developed secondary mineral veinlets described in olivine phenocrysts [1,3]. This study aims to further characterize the ini-tial stages of secondary mineral formation in the mesostasis. Dis-solution processes are also of interest as they contribute signifi-cantly to the chemistry of the putative percolating fluids [3,4].

Application of cathodoluminescence (CL) imaging and spec-troscopy is particularly beneficial for the study of mesostasis minerals as much of the volume is occupied by luminescent phases. CL spectral features are the result of minor and trace element substitutions and/or structural defects. Thus, imaging the distribution of such features may shed light on the nature of aqueous processes in the shallow Martian crust.

Methods: CL data was obtained by using a Gatan MonoCL3+/XiCLone imaging spectrometer mounted on a JEOL 840a SEM. Phase identification was achieved by EDX imaging of major elements. In addition, EMPA and ToF-SIMS analyses provide tests for minor and trace element correlations with CL.

Initial results: Apatite grains are moderate-highly CL lumi-nescent. Further examination is necessary to determine whether the range of CL behavior in phosphates can be ascribed to both primary (high T) and secondary (low T) mechanisms. Feldspars show an even wider range in luminescence. The scale of CL het-erogeneity is evident at both the sub mm-scale (intergrain) within a given mesostasis area and sub µm-scale (intragrain) and is highly correlated with K. Correlated trace element enrichments in alkali feldspars may be responsible for the luminescence. As ex-pected, the Fe-rich minerals that comprise the bulk of nakhlites (clinopyroxene, orthopyroxene, and olivine) show no discernable CL contrast. All CL characteristics observed to date are consis-tent with end-stage solidification of nakhlite melts.

50 µm50 µm50 µm50 µm

fs

cpx apap

mtmtmtfs

fs

fsapap

ol

K-rich fsfsfs

cpx

opx

opx

ol

Fig. 1. BSE image (left) and panchromatic CL image (right) of Lafayette mesostasis.

References: [1] Gooding J. L. et al. 1991. Meteoritics 26, 135. [2] Bridges J. C. and Grady M. M. 2000. EPSL 176, 267-279. [3] Treiman A. et al. 1993. Meteoritics 28, 86. [4] Treiman A. H. and Lindstrom D. J. 1997. GCA 102, 9153.


STRUCTURE AND TEXTURE OF ORGANIC MATTER IN CV AND CO CARBONACEOUS CHONDRITES. RELATIONSHIP TO METAMORPHIC PROCESS. J-N Rouzaud1 , L. Bonal2 and E. Quirico2. 1Laboratoire de Géologie 24 rue Lhomond ENS-Paris Paris France. E-mail: [email protected]. 2Laboratoire de Planétologie de Grenoble Université Joseph Fourier 38041 Grenoble Cedex 9 France.

Insoluble Organic Matter (IOM) in CV and CO carbonaceous

chondrites is polyaromatic. Its degree of structural order is con-trolled by thermal metamorphism on the parent body [1,2]. High Resolution Transmission Electron Microscopy (HRTEM) is a powerful tool which makes possible the imaging of the aromatic layers. The multiscale organization can be directly imaged over 3 orders of magnitude (µm-nm). The structure is the order at the atomic scale within polyaromatic layers, single or stacked, whereas the microtexture corresponds to the spatial orientation of these layers. Based on the knowledge of terrestrial natural or an-thropic carbons, the structure appears to be mainly governed by the temperature, whereas the microtexture (which cannot be as-sessed by Raman spectroscopy) is the fingerprint of the chemical nature of the precursor and of the metamorphic conditions, such as pressure [3]. HRTEM image analysis also provides quantita-tive structural information, thanks to a numerical data treatment [4].

In this study, we have investigated a series of IOM samples extracted from CV and CO chondrites by HRTEM and Raman spectroscopy. The maturation grade of each raw sample have been previously accurately established [1,2]. The HRTEM analy-sis are consistent with earlier works (e.g. [5]). Correlated with the degree of thermal metamorphism experienced by each object, our results show that both structure and microtexture are controlled by thermal metamorphism. The interlayer distance decreases with the metamorphic grade, whereas the layer length and the number of stacked layers increase.

No “onion-like” or “giant fullerenes” features have been ob-served in the less metamorphized objects (e.g. Kaba CV3), unlike in Allende. These features are formed by thermal metamorphism on the parent body. Consequently, the statement that such fea-tures may be the source of the so-called “Q-phase” in these ob-jects [5] should be ruled out. The porous microtexture of the ma-terial suggests a metamorphic process in low pressure conditions, but no quantitative information can be yet obtained.

References: [1] Bonal. et al. 2005 Geochimica Cosmochimica Acta Under revisions ; Bonal et al. 2004 LPSC 2004 abstract #1562. [2] Bonal et al. 2005 LPSC 2005 abstract #1699. [3] O. Beyssac et al (2002). Graphitization in a high-pressure, low-temperature metamorphic gradient : a Raman mi-crospectrometry and HRTEM study. Contrib. Mineral Petrol (2002) 143, 19-31. [4] J.N. Rouzaud et al. Fuel Processing Technology, 77-78 (2002). [5] Vis et al. 2002 Meteoritics and Planetary Sciences 37, 1391-1399.


SHOCK AND ANNEALING IN UREILITES. Alan E. Rubin, Institute of Geophysics, University of California, Los Angeles, CA 90095-1567, USA. ([email protected]).

The thermal and shock histories of ureilites can be divided

into four stages: (1) formation, (2) initial shock, (3) post-shock annealing, and (4) post-annealing shock. Stage 1 occurred ~4.55 Ga ago when ureilites formed by melting chondritic material. Impact events during stage 2 caused silicate darkening, undulose to mosaic extinction in olivines, Fe2+ disorder in pigeonite, and the formation of diamond, lonsdaleite and chaoite from indige-nous carbonaceous material. Alkali-rich fine-grained silicates and a minor LREE-rich phase may have been introduced by im-pact injection into ureilites at this stage. About 55% of the ureilites remained at stage 2 (e.g., ALH 78262, EET 90019, PCA 82506). During stage 3, impact-induced annealing caused previ-ously mosaicized olivine grains to become aggregates of small unstrained crystals. Some ureilites experienced reduction as FeO at the edges of olivine grains reacted with C from the matrix. Annealing may also be responsible for coarsening of graphite in a few ureilites, forming euhedral-appearing, idioblastic crystals. Orthopyroxene in META78008 may have formed from pigeonite during annealing at this stage. The Rb-Sr internal isochron age of ~4.0 Ga for META78008 probably dates the annealing event. At this late date, impacts are the only viable heat source. About 40% of ureilites remained at stage 3 (e.g., ALH 77257, GRA 95205, Nova 001). During stage 4, ~5% of the ureilites were shocked again, as is evident in the polymict breccia, EET 83309. This rock contains annealed mosaicized olivine aggregates com-posed of small individual olivine crystals that exhibit undulose extinction.

Ureilites may have formed by impact-melting chondritic material on a primitive body with heterogeneous O isotopes. Olivine and pyroxene crystallized from the impact melt and set-tled to the floor of the crater. Plagioclase was preferentially lost from the system due to its low impedance to shock compression. Brief melting and rapid burial minimized the escape of planetary-type noble gases from the ureilitic melts. Incomplete separation of metal from silicates during impact melting left ureilites with relatively high concentrations of trace siderophile elements.

Impact-melting processes seem best able to account for the petrogenesis of ureilites. After formation, additional collisions caused shock effects and annealing episodes. Successive impact events are responsible for the myriad textural and compositional properties of this enigmatic group.


A NEW AQUEOUS ALTERATION INDEX FOR CM CARBONACEOUS CHONDRITES. Alan E. Rubin, Josep M. Trigo-Rodríguez and John T. Wasson, Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA. ([email protected]).

CM carbonaceous chondrites exhibit a wide range in their

degree of aqueous alteration. It is probable that the original nebular material had properties consistent with petrographic sub-type 3.0. Acfer 094 may be an example of such material; it ex-hibits little evidence of aqueous alteration [1] and contains nu-merous chondrules with glassy mesostases [2]. It has very high bulk concentrations of presolar diamonds and SiC [3], CM-like Zn and Se contents [4], and a CM-like matrix/chondrule ratio (1.2) [2]. Aqueous alteration in CM chondrites is reflected in the abundance of indigenous water (~9 wt.% H2O+) [5] bound within phyllosilicates (mainly serpentines and montmorillonites). Al-teration products include tochilinite (an interstratified Fe-Ni sul-fide and Fe-Mg hydroxide), hydrated Mg- and Ca-sulfates, and secondary sulfide phases (mainly pentlandite and Ni-bearing pyr-rhotite). Grains of carbonate, clusters of magnetite, and clumps of so-called “poorly characterized phases” (i.e., PCP), consisting mainly of phyllosilicate and tochilinite intergrown with pentland-ite and pyrrhotite, also occur. .

We studied nine CM chondrites that span the range of negli-gible-to-extreme aqueous alteration. We prepared mosaics of back-scattered electron (BSE) images of thin sections of these meteorites with a resolution of 2 µm/pixel, made multi-element x-ray images of selected regions, and analyzed phases with the electron microprobe.

From these and literature data [e.g., 6,7], we identified 11 pa-rameters that reflect progressive aqueous alteration in CM chon-drites: (1) increased formation of phyllosilicates, (2) destruction of isolated matrix silicate grains, (3) alteration of chondrule mesostasis, (4) alteration of chondrule mafic silicate phenocrysts, (5) oxidation of metallic Fe-Ni (first from the host, then from chondrules), (6) decreased abundance of large PCP clumps, (7) increased phyllosilicate/sulfide ratio in PCP clumps, (8) in-creased uniformity in PCP composition, (9) increased PCP for-mation in the outer layers of fine-grained mantles around chon-drules, (10) development of secondary sulfide, and (11) devel-opment of Ca carbonate, followed by complex (Ca,Mg,Fe,Mn) carbonate, and ending in the near-disappearance of carbonate.

On the basis of these parameters, we designed a new aqueous alteration index ranging downward from type-3.0 (pristine, unal-tered materials) to 2.0 (highly altered rocks, currently classified CM1, with essentially no mafic silicates but containing chondrule pseudomorphs composed mainly of phyllosilicate). We assigned alteration subtypes to every CM chondrite that we studied: Acfer 094, “CM”3.0; QUE 97990, CM2.8; Murchison, CM2.7; Murray, CM2.7; Y791198, CM2.7; QUE 99355, CM2.5; Cold Bokkeveld, CM2.2; QUE 93005, CM2.1; LAP 02277, CM2.0.

References: [1] Greshake A. 1997. Geochim. Cosmochim. Acta 61: 437-452. [2] Kunihiro T. et al. 2005. Geochim. Cosmo-chim. Acta 69, in press. [3] Newton J. et al. 1995. Meteoritics 30: 47-56. [4] Spettel B. et al. 1992. Meteoritics 27: 290-291. [5] Jarosewich E. 1990. Meteoritics 25: 323-337. [6] Browning L. et al. 1996. Geochim. Cosmochim. Acta 60: 2621-2633. [7] Hanowski N. P. and Brearley A. J. 2001. Geochim. Cosmochim. Acta 65: 495-518.


Al-26 IN UOC CHONDRULES: IMPRINTS OF THERMAL METAMORPHISM IN A NEBULAR ENVIRONMENT N.G. Rudraswami, J.N. Goswami and M.P. Deomurari. Physical Research Laboratory, Ahmedabad-380009, India. E-mail: [email protected]

26Al records in chondrules provide information on the time

and duration of chondrule formation in the early solar system [1-4]. We have carried out systematic study of Al-Mg isotope sys-tematics in chondrules from unequilibrated ordinary chondrites belonging to various metamorphic grades [LEW86134 (L3.0), ALHA77176 (L3.2), and QUE97008 (L3.4)] to further our un-derstanding about chondrules formation time and the site of thermal metamorphism responsible for resetting Al-Mg systemat-ics in chondrules.

A scanning electron microscope equipped with an energy dispersive X-ray analyzer was used for identification of small areas with high Al/Mg ratio within chondrules; these occur pri-marily in glassy mesostasis. The Al-Mg isotope systematics in these areas, typically less than ten microns, were obtained using a Cameca ims-4f ion microprobe. Multiple analyses were con-ducted at each analyzed spot to improve analytical precision.

Most of the analyzed chondrules are devoid of phases with high Al/Mg ratio. Four chondrules from LEW86134 (L3.0), two from ALHA77176 (L3.2) and six from QUE97008 (L3.4) having areas with high Al/Mg ratios were studied in detail. The well de-fined isochrons observed in three chondrules of QUE97008 (L3.4) yielded (26Al/27Al)o of (1.95±0.38)x10-5, (1.00±0.32)x10-5 and (7.9±1.8)x10-6, respectively. Even though the data for the other three chondrules have large errors, marginal 26Mg excess is evident. In ALHA77176 (L3.2), the (26Al/27Al)o values for two chondrules are (6.3±2.9)x10-6 and (9.5±4.1)x10-6, respectively. In LEW86134 (L3.0) three chondrules show 26Mg excess with (26Al/27Al)o of (1.63±0.36)x10-5, (1.08±0.22)x10-5 and (7.1±2.8)x10-6, while the fourth chondrule yielded an upper limit of 1.6x10-6. This particular chondrule must have had its Al-Mg systematics thermally reset before its incorporation into the par-ent body of LEW86134. Lower values of (26Al/27Al)o were also reported earlier for chondrules from the UOC Semarkona (LL3.0), Krymka (LL3.3), Quinyambie (LL3.4) and Chainpur (LL3.4) [3]. The presence of excess 26Mg with well defined (26Al/27Al)o in chondrules from QUE97008 (L3.4) with values similar to those seen in UOC of lower metamorphic grades sug-gest that parent body metamorphism may not be the major cause of the perturbed Al-Mg systematics in chondrules from UOC of lower metamorphic grade [see, e.g., 3]. We suggest that thermal metamorphism of such chondrules took place in a nebular envi-ronment prior to their incorporation into meteorite parent body.

References: [1] Russell S.S. et al. 1996. Science 273:757-762. [2] Kita N.T. et al. 2000. Geochimica et Cosmochimica Acta 64:3913–3922. [3] Huss G.R et al. 2001. Meteoritics & Planetary Science 36:975–997. [4] Bizzarro M et al. 2004. Nature 431:275-278.


A TERRESTRIAL FRACTIONATION LINE FOR THE OXYGEN ISOTOPES OF PHOSPHATE MINERALS AND ITS APPLICATION TO METEORITES. D. Rumble1, C.M. Corrigan2, R.E. Blake3, and T.J. McCoy2. 1Geophysical Lab, 5251 Broad Branch Rd., NW, Washington, DC, 20015. ([email protected]). 2Dept. of Mineral Sciences, National Mu-seum of Natural History, Smithsonian Institution, Washington, DC, 20560. 3Dept. of Geology and Geophysics, Yale University, New Haven, CT, 06520.

Introduction: Isotope analysis of phosphate minerals for

17O/16O and 18O/16O has proven useful in understanding relation-ships between meteorites [1]. A number of meteorites contain phosphate so sparsely distributed, however, that analysis of min-eral separates would require the disaggregation of unacceptably large amounts of rare specimens. Accordingly, we sought to test in situ analysis for oxygen isotopes with an ultraviolet (UV) laser fluorination isotope microprobe. A daunting problem in laser fluorination of phosphate minerals is that oxygen yields are non-stoichiometric and, therefore, isotope fractionation may result. It is expected that such fractionation would be mass dependent: both δ18O and δ17O are shifted in relation to a mineral’s total oxygen but the value of ∆17O should remain unaffected. The strategy adopted to assess the impact of non-stoichiometric oxy-gen yields was to measure δ18O and δ17O in a variety of terres-trial phosphate minerals and in Ag3PO4 prepared from them in order to learn whether the data define a terrestrial fractionation line (TFL). Given a statistically significant TFL, one can then analyze meteorite phosphate and obtain its value of ∆17O by comparison to the TFL. Conventional analysis of aliquots of phosphate for δ18O may then be used to calibrate the results in relation to VSMOW [2].

Results: Fluorination with infrared and UV lasers of 47 ter-restrial phosphate minerals and Ag3PO4 produced a TFL extend-ing over a range of 40 per mil in δ18O with slope of 0.527 (+/- 0.004) and δ17O-axis intercept of -0.046 (+/- 0.045) with R2 = 0.9975 [3]. The samples analyzed included apatite from coesite-bearing eclogite [4], sarcopside [5], and Ag3PO4 [6]. Data on tooth enamel [7] were included in the regression. The measured slope of 0.527 for phosphate’s TFL is intermediate between high precision measurements of 0.5247 [3] for silicate minerals and 0.528 [8] for meteoric water.

Application to meteorites: Two phosphate inclusions in the iron meteorite EET 83230 were fluorinated with a UV laser and purified F2 gas. Values of δ18O range from +1.8 to +4.8 per mil. Values of ∆17O, however, lie in a much narrower range, from +0.97 to +1.07. It is concluded that laser fluorination can be used to measure ∆17O in meteorite phosphate minerals but that accurate analysis by this technique for δ18O requires calibration.

References: [1] Clayton R. and Mayeda T. 1996. GCA 60: 1999-2018. [2] Vennemann T. et al. 2002. Chem Geol 185: 321-336. [3] Miller M. 2000. GCA 66: 1881-1889. [4] Zhang Z. and Rumble D. 2005. Am Min 90: 857-863. [5] US National Museum [6] R.E. Blake, Yale Univ [7] Jones A. et al. 1999. Chem Geol 153: 241-248. [8] Li W. and Meijer H. 1998. Iso. Env. Health Stud. 34: 349-369.



DISCRIMINATION OF ACAPULCOITES AND LODRANITES FROM WINONAITES. D. Rumble, III1, A. J. Irving2, T. E. Bunch3, J. H. Wittke3 and S. M. Kuehner2, 1Geophysical Laboratory, Washington, DC 20015 [email protected]; 2Earth & Space Sciences, Univ. of Washington, Seattle, WA 98195; 3Dept. of Geology, Northern Arizona University, Flagstaff, AZ 86011.

Introduction: Combined petrological and oxygen isotopic analyses of five Northwest African primitive achondrites (NWA 516, NWA 1457, NWA 1617, NWA 2627 and NWA 2656) have clarified the relationships among acapulcoites, lodranites and winonaites. It would not be possible to properly classify some specimens in these groups using their mineral compositions alone (see plot below).

Petrology: These new specimens have polygonal-granular textures (grainsize 0.4-0.8 mm) and lack chondrules. Mineral compositions are, respectively: orthopyroxene Fs 1.25, 6.2, 11.2, 12.3, 8.4; olivine Fa 1.03, 5.2, 11.6, 13.1, 8.0; plagioclase An 9.5, 14, 16, 20.9, 22, with metal, troilite and schreibersite. NWA 516, 1457 and 2656 contain Cr-diopside (Fs0.76Wo45, Fs2.8Wo44, Fs3.8Wo44, respectively); NWA 1457, 1617 and 2656 contain chromite (Cr/(Cr+Al) = 0.87, 0.89, 0.85, respectively); NWA 1457 contains minor Cl-apatite and thin daubreelite blades in troilite.

NWA 1463 is a Type 5 metal-rich chondrite with a recrystallized matrix proposed by [1] to be related to the winonaite parent body. A sample provided to us by D. Gregory contains Fa5.9 olivine (more ferroan than reported by [1]), and has, respectively, δ18O = 2.92, 3.18, 3.44; δ17O = 1.10, 1.24, 1.40; ∆17O = -0.45, -0.44, -0.42 per mil.

30

Fa, mole%

-1.6

-1.2

-0.4

0

0 5 10 15 20 25

∆17O

, per

mil

-0.8

LOD/ACAP

Winonaites

Lodranites

Acapulcoites

150026271617

1058

2656

516

22351052

1457

MD

Y74063

MM

P

1463

P = Pontlyfni MM = Mount Morris (WI) MD = Monument Draw

WIN

Olivine and oxygen isotopic compositions for primitive achondrites and related chondrites (circles). Numbers refer to NWA specimens. Data from this work and [2].

References: [1] Benedix G. et al. 2003 66th Met. Soc. Mtg., #5125 [2] Benedix G. et al. 1998 GCA, 62, 2535-2553; Clayton R. and Mayeda T. 1996 GCA, 60, 1999-2018; yamato.nipr.ac.jp/AMRC/AMRC/meteoritelist.pdf; Bartoschewitz R. et al. 2003 66th Met. Soc. Mtg., #5114; Mittlefehldt D. and Hudon P. 2004 67th Met. Soc. Mtg., #5086; Russell S. et al. 2004 Met. Bull. 88; Moggi-Cecchi V. et al. 2005 LPS XXXVI, #1808.


GEOCHEMICAL CONSTRAINTS FOR THE ORIGIN OF THE STEINBACH (IVA) STONY IRON METEORITE. A. Ruzicka and M. Hutson. Cascadia Meteorite Laboratory, Port-land State University, Dept. of Geology, Portland, OR 97207.

Introduction: We analyzed the unusual Steinbach stony-

iron meteorite, which appears to belong to the IVA iron group despite having abundant ortho- and clinobronzite (low-Ca px) and tridymite [1,2], by using SEM, EMPA, and LA-ICP-MS techniques. Steinbach may have formed either by metal-silicate mixing during a parent-body break-up and reassembly event [2,3], or by incorporating evolved silicate melt inside a core dur-ing solidification shrinkage of the core [4]. Our LA-ICP-MS data for low-Ca px and chromite (chr) represent the first in situ trace-element data obtained for this unusual meteorite, and to-gether with other observations, constrain its petrogenesis.

Chemical variability of low-Ca px: Low-Ca px shows variations in the concentrations of various elements. For exam-ple, abundances vary by a factor of ~2-3x for Al, Ca, Ti, V, Cr, Y, and Sc, with most of this variation occurring between differ-ent grains, although modest core-to-rim or unidirectional intra-grain zoning is also observed. Cobalt and Ni abundances appear to vary more greatly (by up to ~10x), although some of this variation is caused by the clouding of grains by troilite inclu-sions. Evidence for chemical variability implies that metamor-phism has not erased compositional gradients in pyroxene. Ob-served variations are consistent with mineral-melt partitioning and suggest that “clouded” and clinobronzite grains crystallized at an early stage. The chemical variability also implies that a restite origin for Steinbach is unlikely. In agreement with others [4], we instead favor a cumulate origin for Steinbach, with dif-ferent grains forming at different times in an evolving magmatic system.

Parental melt: We estimated the composition of the Stein-bach parental melt by combining our data for low-Ca px and chr with mineral-melt partition coefficients obtained from the litera-ture. This melt appears to have had a generally chondritic com-position (~1 x CI) for semi-compatible elements (Sc, V), possibly modest enrichments (~0.6-2.5 x CI) for moderately incompatible elements (Ti, Y, Yb), and slight enrichments (~2-6 x CI) for highly incompatible elements (Nb, Zr, Ce, Nd). These character-istics are consistent with the crystallization of Steinbach from a partial melt, albeit one that was fairly depleted in incompatible elements.

Origin of Steinbach? Our geochemical data and the miner-alogy of the meteorite imply that Steinbach precursor materials must have lost a more evolved melt fraction, before the precursor melt formed out of which Steinbach crystallized. This requires a two-step melting process, either two distinct events or one pro-tracted melting event with increasing temperatures. It is as yet unclear whether this two-step melting process and cumulate ori-gin is consistent with proposed models for Steinbach.

References: [1] Scott E.R.D. et al. (1996) Geochim. Cosmo-chim. Acta 60:1615-1631. [2] Haack H. et al. (1996) Geochim. Cosmochim. Acta 60:3103-3113. [3] Wang. P-L. et al. (2004) Geochim. Cosmochim. Acta 68:1159-1171. [4] Ulff-Møller et al. (1995) Geochim. Cosmochim. Acta 59:4713-4728.


WIDESPREAD ALUMINIUM-26-INDUCED MELTDOWN OF PLANETESIMALS AND AN EMERGING RATIONAL EARLY SOLAR SYSTEM CHRONOLOGY. I. S. Sanders, Department of Geology, Trinity College, Dublin, Ireland. E-mail: [email protected]

Inescapable heating: Corroboration of the Al-Mg chronometer

by precise Pb-Pb dating implies that at the time of CAI formation (t = 0) 26Al/27Al was 5 x 10-5 throughout the nebular dust in the feed-ing zone of the meteorite parent bodies. This level of radioactivity translates to about 9 kJ g-1 of energy in ‘dry’ dust, well in excess of the 1.6 kJ g-1 needed to heat cold dust to total melting. A further 2 kJ g-1 may have been present in 60Fe. Hence planetesimals that accreted during the first two million years (Myr) almost certainly melted (the half-life of 26Al is 0.73 Myr).

Molten planetesimals: Numerical modeling [1,2] suggests that larger bodies (e.g. radius = 50 km) which fomed in the first 1 or 1.5 Myr rapidly became (and remained, perhaps until 2.5 Myr) globes of convecting magma encased within thin rigid crusts. Smaller bod-ies (e.g. radius < 10 km) or those formed after about 2.5 Myr would not have melted. Since most parent bodies (80% of them) did, evi-dently, melt [3] it seems that the early disk was populated with abundant thin-skinned molten spheres.

Chondrule origins? Did such bodies collide with each other from time to time, showering the nebula with cascades of molten droplets that froze and later accreted to other planetesimals? Could such droplets be preserved today as chondrules? Near-total melting would have meant that the droplets had primitive chemistry, not unlike that of chondrules. Also, perhaps, impact splashing hap-pened for as long as active heating kept the crusts thin, perhaps for the first 2.5 Myr, and that accretion and meltdown destroyed most droplets that were made during the first 1.5 Myr. It may be no co-incidence that chondrule ages, almost 50 of which have now been published, cluster between 1.5 and 2.5 Myr.

These observations invite research on the detailed evolution of molten planetesimal interiors, and the evolution of post-impact plumes. The results of such research will, perhaps, be reconcilable with many aspects of chondrules, including their chemistry, sizes, textures, associated dust, moderately volatile element abundances, inferred cooling rates, and the bulk chemistry of their host meteor-ites.

Later events: The melting model implies that the 20% of par-ent bodies that did not melt (the chondrite parent bodies) accreted after the accretion of differentiated parent bodies (unless, perhaps, they were too small to insulate themselves adequately). Chondrite accretion after about 2.5 Myr is, of course, consistent with meas-ured chondrule ages.

Basaltic lava flowed on the surface of the HED parent body at about 3 Myr. Perhaps this body accreted rather late, at 1.5 to 2 Myr, and thus heated up so slowly that wholesale internal convec-tion did not ensue, and instead basalt partial melt had time to mi-grate upwards [4]. Could the crystallization of all asteroidal basalt date from about 3 Myr [5], with much younger ages corresponding to later isotopic re-setting?

References: [1] Hevey, P. J. & Sanders I. S. 2005 M&PS (submitted). [2] Sanders I. S. & Taylor G. J. 2005 Astronomical Society of the Pacific: Conference Proceedings (in press) [3] Mei-bom A. & Clark B. E. 1999. M&PS 34:7-24. [4] Taylor G. J. et al. 1993 Meteoritics 28:34-52. [5] Bizzarro M., Baker J. A. and Haack H. 2005 Abstract #1312. 36th Lunar and Planetary Science Confer-ence.


Cl-AMPHIBOLE IN MELT INCLUSION FROM MIL 03346 : EVIDENCE FOR MARTIAN SOIL ASSIMILATION. V. Sautter1, A. Jambon2 and O. Boudouma3. 1Laboratoire de Minéralogie, Museum National d'Histoire Naturelle, CNRS UMR 7160,Paris. 2Laboratoire MAGIE, Université P. et M. Curie, Paris. 3UFR des Sciences de la Terre, Université P. et M. Curie, Paris.

MIL 03346, the newly found nakhlite from Antarctica,

exhibits large augite phenocrysts (72%) and rare (less than 4 %) porphyritic olivine (up to 1mm) set in an abundant (24%) dark mesostasis (20%) with subsidiary phases showing quench textures. The present work focuses on the vitrophyric melt inclusions (MI) trapped in augite and olivine cores. Their sizes range 50-500 micrometers. Most of them display an overall composition similar to the mesostasis once recristallization of the host crystal is taken into account. A small number (about 20% of the MI in our section of about 1 cm2) exhibits however unusual mineralogy and chemistry.

Mineralogy: beside augite, olivine, silica-rich phase, low Ca pyroxene and oxides common to most of MI, we found exotic minerals such as Cl-rich amphibole, chlorite, and phosphate. A mixed sulfate of Fe and S has also been observed. They gather in three types of MI: (I) standard MI with mineral composition similar to the mesostasis; (II) olivine-hosted MI with Cl-amphibole, chlorite, chromite and Cl-apatite; (III) augite-hosted MI with Cl-amphibole, K rich-glass, Fe-Ti oxide and sulfate.

Chemistry: several odd features are observed in type II and type III MI. The amphibole, a ferropargasite, is zoned and contain up to 7% Cl. It thus differs from the Ti-rich amphibole (kaersutite) described previously in MI within basaltic shergottites and Chassigny [1]. The abundance of sulfur in the glass exceeds that expected for a melt in equilibrium with iron sulfide and containing about 60% silica. The chlorine content in the glass of about 5000 ppm is a rather high value. When added to chlorine from the amphibole (3.5% on the average), it gives a Cl concentration in the inclusion that largely exceeds 2 %, a reasonable Cl content for a melt.

Interpretation: composition variability of MI indicates that they cannot result from a single entrapment episode of an early melt. At least, another component is required which contains significant amounts of Cl and S as sulfate. A fluid phase can be excluded since the odd phases are never observed as fracture filling materials, along mineral boundaries or as patches within the mesostasis. We know from in situ analyses of the Martian soil that abundant chloride and sulfate are present at the surface [2].Therefore a small amount of soil component could have been trapped within the lava flow upon eruption. Small particles were trapped with melt as magmatic inclusions in phenocrysts. Their subsequent reaction with the melt resulted in the odd mineralogy described above. In the remaining melt (mesostasis), this contamination remained cryptic due to dilution effect. Our interpretation confirms that nakhlites represent a thick lava flow erupted at the surface of Mars. Their secondary hydrothermal alteration results from reactions at the surface and could therefore evidence melting of the pergelisol below the magmatic pile.

References : [1] McSween H.Y. and Treiman A.H. 1998, MSA rev in Min. 36,6-01-6-40 [2] Reider R. et al. 2004, Science 306, 1746-1750.


CHEMICAL EVIDENCE OF ASTEROIDAL FRAGMENTS (IRON METEORITES AND/OR PALLASITES) IN THE EARTH'S UPPER CONTINENTAL CRUST? G. Schmidt1,2, H. Palme3, K.-L. Kratz2. 1Max Planck Institut für Chemie, Mainz. 2Institut für Kernchemie, Universität Mainz. E-mail: [email protected]. 3Institut für Geologie und Mineralogie, Universität zu Köln.

Introduction: The noble metal composition of the Earth's

upper continental crust is essential for understanding its origin and the processes by which it formed. It is well known that the Moon was subjected to intense post-accretionary bombardment [1]. After formation of the Moon, a feldspathic crust formed the lunar highlands around 4.44 ± 0.02 Ga [2] with evidence for a short and intense late heavy bombardment period, around 3.85 Ga [3]. During solidification of the Earth’s crust the surface was exposed to a similar flux of impacting asteroidal fragments as the Moon. In principle, chemical evidence of asteroidal fragments in crustal material should therefore be seen in the abundance pattern of Os, Ir, Ru, Rh, Pt, Pd, and Ni.

The abundances of Rh, Ru, Pt, and Pd in the Earth’s upper continental crust (UCC) are not well known. An estimation of the average Rh, Ru, Pt, and Pd composition of the exposed crust is difficult because of the geological complexity and therefore het-erogeneous composition. Reliable literature data on metamorphic rocks are rather rare. A far more complicated issue is the average noble metal element composition of middle, lower, and bulk con-tinental crust. However, hypervelocity impact events on Earth affected a large volume of the Earth’s crust and produce chemi-cally homogeneous melt sheets which are mixtures of all litholo-gies involved. The contents of Os, Ru, Rh, Pt, and Pd in such mixtures involving material possibly to a depth of ~28 km can be derived from melt sheets by Ir regression lines (to Ir equals zero) from the Y-axis intercepts.

Results: Average noble metal abundances in the UCC de-rived from European melt sheets, crater suevites and basement rocks from the Ries crater are as follows: 30 ± 50 pg/g Os (N=10), 14 ± 8 pg/g Ir (N=48), 1.0 ± 0.6 ng/g Ru (N=33), 0.4 ± 0.2 ng/g Rh (N=11), 1.5 ± 0.6 ng/g Pt (N=22), and 2.0 ± 0.5 ng/g Pd (N=11). Elemental ratios of Os, Ir, Ru, Pt, Rh, and Pd in the UCC are highly fractionated, compared to the Earth’s mantle [4]. The abundance distribution apparently indicates two groups of elements; (1) Os and Ir and (2) Ru, Pt, Rh, Pd, and Ni. The frac-tionation pattern from some pallasites and magmatic iron meteor-ites seem most compatible with our present data on the UCC. The present noble metal and Ni composition of the UCC probably preserves an imprint of a magmatic crystallisation process, result-ing in fractionation of the compatible (Os, Ir) from the more in-compatible elements (Ru, Rh, Pt, Pd, Ni). One possible explana-tion is that these elements have been added during solidification of the growing Earth’s crust by impacts of IIIAB iron and/or pallasitic bodies. In future studies, noble metal analyses of palla-sites should be supplemented for Rh, since there are only few data on Rh in the literature.

References: [1] Neukum G. et al. 1975. Proc. Sixth Lunar Sci. Conf., Geochim. Cosmochim. Acta. 6:2597-2620. [2] Carlson R.W. and Lugmair G.W. 1988. Earth and Planetary Science Let-ters 90:119-130. [3] Ryder G. et al. 2000. In: Origin of the Earth and Moon, University of Arizona Press, Tucson, pp. 475-492. [4] Schmidt G. 2004. Meteoritics & Planetary Science 39:1995-2007.


PETROGENESIS OF APOLLO 15 OLIVINE- AND QUARTZ-NORMATIVE MARE BASALTS. D. W. Schnare1, L. A. Taylor.1, J. M. D. Day1, M. D. Norman2 Planetary Geo-sciences Institute, University of Tennessee, Knoxville, TN, 37996 E-mail: [email protected] 2Australian National Univer-sity, Canberra ACT 0200, Australia.

Introduction: Mare basalts are important lunar samples be-

cause of the mineralogical and chemical information they yield about their mantle source regions. On the basis of petrography and chemistry, most of the Apollo 15 mare basalts have been as-signed to one of two groups: olivine-normative and quartz-normative basalt [1,2]. We present results of a detailed major- and trace-element study of mineral phases in four Apollo 15 mare basalts (15016, 15475, 15499, 15555). Polished thin sec-tions of these samples were studied to examine their mineral chemistry and modal distributions. Polished thick sections of two olivine-normative basalts (15016-221, 15555-955) and two quartz-normative basalts (15475-174, 15499-154) were prepared for electron microprobe and laser ablation ICP-MS (LA-ICP-MS) analyses.

Methods: Mineral major-element compositions were meas-ured using an automated CAMECA SX-50 electron microprobe (EMP). Mineral trace-element compositions were measured by LA-ICP-MS at the Australian National University, Canberra.

Discussion: Apollo 15 olivine- and quartz-normative mare basalts have identical crystallization ages (~3.3±0.1 Ga [3,4,5]), and similar whole-rock rare-earth-element patterns. Olivine-normative basalts possess olivine with Fo25-60, and pyroxenes compositions ranging Wo10-42En10-59Fs22-55. The quartz-normative basalts have olivine compositions of Fo44-69, and pyroxene in the range of Wo5-40En13-67Fs25-43, consistent with previously pub-lished data [6,7]. Despite having many features in common, the two groups are unlikely to be related to each other by simple fractionation from a common parental magma or by differential partial melting of a common mantle source [2,8]. This study ad-dresses the relationship of Apollo 15 olivine-normative and quartz-normative basalts using an in-situ mineralogic approach to understand the causes of chemical dispersion in the olivine- and quartz-normative basalts. Using our LA-ICP-MS data in conjunc-tion with published experimental partition co-efficient mineral phase data we calculate incompatible element parental melt com-positions for quartz- and olivine-normative Apollo 15 basalts to more fully understand the complex relationships between these suites of rock.

References: [1] Dowty E. et al. 1973. Proc. Lunar Sci. Conf. 4th, 423-444. [2] Rhodes, J. M., Hubbard, N. J. 1973. Proc. Lu-nar Sci. Conf. 4th, 1127-1148. [3] Nyquist, L. E., Shih, C. Y. 1992. Geochimica et Cosmochimica Acta, 56, 2213-2234 [4] Snyder G.A. et al. 1997. Lunar Planet. Sci. Conf. XXVIII, 1347-1348. [5] Snyder G.A. et al. 1998. Lunar Planet. Sci. Conf. XXIX, abstract #1141. [6] Ryder G. (1985), Catalog of Apollo 15 Rocks, pp. 1296. [7] Shervais J.W. et. al. 1990. Proc. Lunar Planet. Sci. Conf. 20th, 109-126. [8] Chappell, B. W., and Green, D. H. 1973. Earth and Planetary Science Letters, 18, 237-246.


SI IN METAL OF CR-CHONDRITES: INDICATOR FORINCOMPLETE METAL-SILICATE EQUILIBRATION ATHIGH COOLING RATES. Th. W. Schoenbeck and H. Palme.University of Cologne, Institute of Geology and Mineralogy,Zuelpicher Str. 49b, 50674 Cologne, Germany. E-mail:thorbjoern.schoenbeck @uni-koeln.de.

Introduction: CR chondrites contain abundant FeNi metalwithin chondrules. The partitioning of normally lithophiletrace elements (Cr, Si, P, V and Mn) between chondrule metaland liquid silicates is controlled by temperature and oxygenfugacity during chondrule formation [1,2], as well as by thecooling rate during subsequent cooling. Trace elements inAcfer 209 chondrule metal were determined by electron mi-croprobe. The detection limit of Si was 50 ppm. Analyticaluncertainties are less than 10% at concentrations above 100ppm [3]. After analysis, metal was etched to reveal metal-lographic structures.

Results: Trace element contents in metal are highly vari-able from grain to grain [3] but homogeneously distributed insingle grains, except for Si, which is highly variable evenwithin single grains (between 50 ppm and 1500 ppm on a 10-µm scale, see Fig.) Some chondrule metal shows taenite-kamacite exsolution.

Discussion: The high variation of Si in contrast to Cr orCo is the result of metal-silicate equilibrium at different tem-peratures. Unlike Cr or Co, Si metal-silicate partition coeffi-cient decreases with decreasing temperature. Thus, high Siconcentration reflects equilibration at ~1700 K, low Si con-centration indicates ~1400 K. FeO contents of olivine and py-roxene in chondrules were used as temperature-independentindicator for fO2 during chondrule formation. The average FeOin chondrule olivine of ~2 wt% corresponds to a fixeddust/gas ratio of approximately 50x CI.

High local Si contents in single grains are only preservedat high cooling rates. Hence, trace elements in chondrule metalindicate cooling rates above 750 K/hour between 1600 K and1100 K. Taenite-kamacite exsolution in chondrule metal re-flects much slower cooling at temperatures below 1100 K.

References: [1] Connolly, H. C. et al. 2001. Geochimica etCosmochimica Acta 65:4567-4588. [2] Zanda, B. et al. 1994.Science, 265:1846:1849. [3] Schoenbeck, Th. W. and Palme, H.2004. Abstract #1706, 35th Lunar and Planetary Science Con-ference.


PALLADIUM — SILVER SYSTEMATICS OF THE EARLY SOLAR SYSTEM. M. Schönbächler1, R. W. Carlson1 and E. H. Hauri1 1Dept. of Terrestrial Magnetism, Carnegie Insti-tution of Washington, 5241 Broad Branch Road, NW, Washing-ton, DC 20015, USA). E-mail: [email protected]

The extinct radionuclide 107Pd decays to 107Ag with a half-

life of 6.5 Myrs and is a useful chronometer to study early solar system processes. In particular, Pd-Ag has been successfully ap-plied to study the formation and differentiation of iron meteorites [1-3]. Internal isochrons determined for these meteorites gener-ally yield initial 107Pd/108Pd ratios in the range of 1.5 – 2.5 × 10-5 [1-3]. However, because it is difficult to obtain precise absolute ages for iron meteorites, it is unclear how precisely these results reflect the initial 107Pd abundance in the solar system.

Troilites from the group IA iron meteorite Canyon Diablo show a negative ε107Ag of ~ -12 [2]. This is the lowest value so far measured for solar system material and is supported by the internal isochron of the Pallasite Brenham that defines an initial ε107Ag (107Ag/109Ag) in the same range. Combining the Canyon Diablo sulfide data with those for whole rock Allende reported by [3] implies, that the solar system started with a high initial 107Pd/108Pd in the range of ~10-4. This high initial 107Pd/108Pd would entail that most iron meteorites reached closure tempera-ture for Pd-Ag only as long as 20 Myr after the solar system formed.

Investigations of Canyon Diablo troilites by others [3] yielded a larger range of ε107Ag (+ 1.0 to -6.0) that does not sup-port the low values reported by [2]. This suggests that at least some Canyon Diablo troilites may be disturbed and have suffered from redistribution of Ag with the surrounding metal. To further investigate the properties of troilites in iron meteorites regarding their closed system behavior and to better constrain the initial 107Pd/108Pd of the solar system, we will perform new Ag isotopic analyses on a range of chondrites and iron meteorite samples.

Silver isotopic analyses are challenging because Ag has only two isotopes. To control the mass fractionation induced by the MC-ICPMS, external normalization relative to Pd and sample-standard bracketing is applied. Prior to the measurements, Ag is separated from the sample matrix by ion-exchange chromatogra-phy. The analytical procedure adapted by [2,3] was further im-proved for chondrites to assure a good separation from Ti.

References: [1] Chen J. H. and Wasserburg G. J. (1996), in

Earth Processes: Reading the Isotopic Code, Geophysics Mono-graph ’95, pp. 1-20. [2] Carlson R. W. and Hauri E. H. (2001) Geochimica and Cosmochimica Acta, 65: 1837-1848. [3] Wood-land S. J. et al. (2005) Geochimica and Cosmochimica Acta, 69:2153-2163


CHARACTERIZING A MODEL SAMPLE FOR DESERT WEATHERING INFLUENCE ON NOBLE GASES IN MARTIAN METEORITES. S. P. Schwenzer, J. Huth, S. Herrmann and U. Ott. Max-Planck-Instiut für Chemie, Becherweg 27, D-55128 Mainz, Germany, [email protected]

Introduction: In interpreting noble gas data from Martian

meteorites the diagram 129Xe/132Xe vs. 84Kr/132Xe is widely used, usually showing three endmembers: Martian interior [1], Martian atmosphere [2] and terrestrial air. In our first study of the influ-ence of desert weathering on the measured signatures Mohapatra et al. [3] showed that elementally fractionated Kr and Xe could cause a signature, which within error plots on the same spot as Martian interior. In [3] we defined the 84Kr/132Xe of EFA (ele-mentally fractionated air) = 1.2. Extending on this observation, we investigated caliche (almost stochiometric calcite [4]) from the surface of SaU 008. In our experiment we found 84Kr/132Xe ratios even lower than the defined EFA ratio [5]. To avoid any meteoritic (Martian) contribution, we also measured the noble gases of a soil sample collected at the find location of SaU 008, which again showed the low 84Kr/132Xe [6]. Here we present our efforts to make this soil sample a model sample for the study of influences from desert weathering on the noble gas budget of Martian meteorites.

Mineralogical characterization: We split our sample into three fractions: >500 µm, 100–500 µm and <100 µm. About 50 % of the sample belongs to the finest fraction. We used the frac-tion 100–500 µm (which makes up about 27 % of the sample) for our investigation. The medium grained fraction contains quartz, mostly coated with carbonate, primary carbonate grains and a small amount of accessory minerals, one of which is Fe-(Cr-)-oxide, most probably spinel.

Leached sample: To separate the noble gas signature of car-bonate from quartz, we tried a leaching experiment. It turned out, however, that the inventory of the leached sample was dominated by laboratory-adsorbed heavy noble gases. An interesting feature is the behaviour of 4He. While in the original soil the amount of 4He reaches its maximum in the 1200 °C step, only a small amount is released from the leached sample at 1200 °C. There-fore we speculate the Fe-(Cr)-oxide to be the source of 4He in the 1200 °C step, which we plan to check by mineral separation.

Re-measuring the soil: As our first soil sample suffered from low amount of sample, we re-measured the Oman Soil with a larger amount of sample (25 mg) in 6 T-steps: 400, 800, 1000, 1200, 1600, and 1800 °C (the last showing blank amounts only). In the first two steps we observed 84Kr/132Xe ratios of 1.28 and 2.31, respectively. In the 1000 °C step the lowest ratio of 0.35±0.10 was observed. The following steps (1200 and 1600 °C) showed slightly higher 84Kr/132Xe ratios. Further, we observed negative δ15N ratios in the first two steps. These nitrogen signa-tures are of special interest, as they also can lead to confusion with Martian interior signatures. They are rare on Earth, but have been observed in nitrates from hot deserts [7].

References: [1] Ott U. 1988. GCA, 52: 1937–1948. [2] Bogard D. D. & Garrison D. H. 1998. GCA., 62: 1829–1835. [3] Mohapatra R. K. et al. 2002. LPSC, XXXIII: # 1532. [4] Dreibus, G. et al. (2000): MAPS, 35: A49. [5] Schwenzer, S. P. et al. (2002) GCA, 66 (Suppl.): A693. [6] Schwenzer, S. P. et al. (2003) LPSC, XXXIV, Abstr. # 1694. [6] Böhlke J. et al. 1997. Chem. Geol., 136: 135–152.


CHONDRITE EVIDENCE FOR ACCRETION OF IMPACT DEBRIS IN THE PROTOPLANETARY DISK. Edward R. D. Scott and Alexander N. Krot. Hawai’i Institute Geophysics and Planetology, University of Hawai’i, Honolulu, HI 96822, USA. Email: [email protected]

Introduction: Chondrules and matrix accreted into planetesi-

mals 1-3 Myr after CAIs formed, consistent with the inferred the lifetimes of T-Tauri stars and protostellar disks. After losing their primordial gas-dust disks, many young stars are thought to develop debris disks from colliding planetesimals perturbed by planetary embryos and planets [e.g., 1]. We review three cases where chon-drites may have accreted planetesimal impact debris in the pres-ence of nebula gas.

Dark clasts: Some altered dark chondritic clasts may be de-rived from near-surface regions of the parent asteroid, or from hy-pervelocity impact of CM-like projectiles impacting regolith long after accretion. But many type 2-3 chondrites contain dark clasts with sizes of 0.1-1 mm that are correlated with host chondrule size; some have matrix rims [2]. These clasts may be fragments of al-tered planetesimals that spiraled in from beyond the snowline and accreted with chondrules.

CB chondrites: These formed by accretion of CAIs, fragments of O and C chondrites, and unique non-porphyritic chondrules with similar ∆17O and Fe,Ni grains, which formed by condensation and melting in a dust-free region of the nebula 5 Myr after CAIs formed [3, 4]. The CB chondrules and Fe,Ni grains, which are to-tally different way from those in other chondrites (except CHs), formed either from impacts of planetesimals of embryos that formed in a massive asteroid belt, or from an unknown heat source that locally vaporized all nebular solids.

Kaidun: The Kaidun chondrite is composed entirely of mm-sized fragments of 7 groups of E, O, and C chondrites, ungrouped C1 and C2 chondrites, and igneous clasts [5]. The variety and size of the fragments may result from turbulent accretion of planetesi-mal fragments from the nebula after chondrule formation had ended, but before gas was lost [2].

Discussion: We suggest that dark clasts represent impact debris that accreted with chondrules 1-3 Myr after CAI formation, whereas for Kaidun and CB chondrites impact debris accreted 1-2 Myr after normal chondrule formation ended. Two possible modes of accretion from nebula gas can be envisaged for Kaidun and CB chondrites: accretion to the surface of a preexisting planetesimal [6], or accretion into planetesimals in an unoccupied zone in the asteroid belt free from gravitational perturbations from planetary embryos and Jupiter. The latter explanation is preferred as these chondrites lack possible host rock types. We infer several stages in the nature of nebular solids during a transition from primordial dust disk to debris disk before gas loss in the asteroid belt: 1) chon-drules and matrix dust with a minor debris (most chondrites); 2) impact debris from numerous collisions of diverse chondritic aster-oids and a few differentiated bodies (Kaidun); 3) impact debris from single large events (CB chondrites).

References: [1] Liu M. 2004. Science 305:1442-1444. [2] Scott E. R. D. and Krot A. N. 2003. In Treatise on Geochemistry, A. M. Davis ed, Elsevier, pp. 143-200. [3] Rubin A. E. et al. 2003. Geochimica et Cosmochimica Acta 67:3283-3298. [4] Krot A. N. et al. 2005. Nature, in press. [5] Zolensky M. E. and Ivanov A. V. 2003. Chemie der Erde 63:185-246. [6] Whipple F. L. 1972. In From Plasma to Planet, ed. A. Elvius, Nobel Symposium 21, Wiley, pp. 211-232.


LITHIUM ISOTOPE COMPOSITIONS OF MARTIAN AND LUNAR RESERVOIRS. H.-M. Seitz1*, G.P Brey, S. Weyer, S. Durali, U. Ott*, C. Münker. 1Inst. f. Mineralogie, Univ. of Frankfurt, Senckenberganlage 28, 60054 Frankfurt, *Max-Planck-Inst. f. Chemie, Mainz, Germany. [email protected].

Introduction: With respect to the behaviour of Lithium isotopy, the early accretion history, the evolution of terrestrial planets and planetesimals and the bulk composition of the solar system is poorly understood. So far, Li isotope studies on extraterrestrial material are scarce, e.g. [1-4]. As to whether the reservoirs of the terrestrial planets differ in their δ7Li iso-topic signature to the earth mantle reservoirs and to what extent these signatures reflect the bulk solar composition, we determined Li-isotopes (MC-ICP-MS) on high-Ti and low-Ti mare basalts, KREEP-rich highland breccias, orange and green glass, and the martian meteorites, Shergotty, Nakhla, Zagami, Lafayette, EETA 79001A, ALHA 77005 and ALHA 84001.

Results: The basaltic shergottites depict a narrow range in their δ7Li-values (+3.6 to +5.2‰). While the lherzolitic sher-gottite and the clinopyroxenite samples show similar δ7Li-values (+4.1 to 5.0‰), the orthopyroxenite ALHA 84001 has a much lighter isotopic signature (δ7Li -0.6‰).

Samples from Moon depict large variation in Li-content (5-49 ppm). With the exception of a KREEP highland breccia (15445), which has a δ7Li-value of +18.3‰, Li-isotope varia-tion is very limited (+3.9 to +6.6‰) with an average of +5.1‰ (1.8, 2σ).

Summary: Neither lunar samples nor SNC meteorites ex-hibit a correlation between their Li-abundances and their Li-isotopic signatures, suggesting that Li isotopes do not fraction-ate during magmatic differentiation. The majority of the lunar basalts investigated here have δ7Li-values around +5.1‰, similar to melts from the Earth mantle, such as MORB and OIB e.g. [5]. Li abundances and isotopic signatures of the basaltic and lherzolitic shergottites are also very similar to the values of C1 chondrites, fresh MORB and bulk silicate earth (BSE) [1,5,6]. It is inferred that the primitive reservoirs of the terrestrial planets have an unfractionated Li-isotopic signature of around δ7Li (+4‰). This value may further reflect the iso-topic signature of the early solar system.

References: [1] James R.H. and Palmer M.R. 2000. Chemical Geology 166: 319-326. [2] McDonough W.F. et al. 2003. Lunar and Planetary Science XXXIV, 1931 pp. [3] Chauissidon M. et al. 2001. XXXII Lunar and Planetary Sci-ence Conference, Abstr. #1862. [4] Beck P. et al. 2004. Geo-chimica et Cosmochimica Acta 68(13): 2925-2933 [5] Chan, L.-H et al. 1992. Earth and Planetary Science Letters 108, 151-160 [6] Seitz H.-M. et al. 2004. Chemical Geology 212, 163-177.



THE PROBABLE PRIMITIVE H-MATERIAL IN THE KRYMKA CHONDRITE. V. P. Semenenko1 and A. L. Girich1. 1Institute of Environmental Geochemistry NAS of Ukraine, Palladina 34a, Kyiv-142, 03680 Ukraine. E-mail: [email protected].

Fine-grained, lithic xenoliths are quite abundant in the

Krymka (LL3.1) chondrite. Most of them have a carbonaceous nature. Due to their exotic mineralogy [1, 2] or unusual textural features [3, 4] they are of a high scientific interest.

Here, we present the results of a preliminary mineralogical and chemical study of the Krymka fine-grained, dark xenolith BK16. Its bulk chemical composition, taken by an electron-microprobe corresponds to 32.4 SiO2, 1.84 Al2O3, 21 MgO, 0.31 MnO, 0.09 TiO2, 1.58 CaO, 34.8 FeO, 0.55 Cr2O3, 0.35 Na2O, 0.05 K2O, 1.06 Ni, 2.41 S, 0.21 P2O5; total 96.6 wt.%; FeO/(FeO+MgO)=0.62. The low analytical total is mainly caused by the porosity of the groundmass, the presence of iron hydroxides and phyllosilicates. Based on the SiO2/MgO-ratio (1.54) a relationship to H-chondrites (1.55 ± 0.05) is suggested.

BK16 consists of three main components (fine-grained matrix, minor coarse grains, and rare chondrules and microchondrules) and has a complicated mineralogy of very fine intergrowths. The matrix is made of olivine (Fa37-49), pyroxene, abundant Fe,Ni particles, minor iron sulfide, rare merrillite, perovskite (59 TiO2, 40.6 CaO, 1.49 FeO, 0,34 P2O5, 0.16 SiO2, 0.12 Al2O3, 0.06 MgO; total 101.8 wt%), and calcite (51.2 wt.% CaO). Coarse grains include pyroxenes (Fs1.43-19.6 Wo0-1.48 and Fs2.8-3.2 Wo6.7-49.3), olivine (Fa0.93-16.0), Fe,Ni metal, iron sulfide, feldspar (Ab18.2-43.6Or0.11-4.2), and rare spinel (71.1 Al2O3, 26.5 MgO, 0.87 FeO, 0.17 TiO2, 0.07 CaO, 0.07 SiO2; total 98.8wt.%). Studied chondrules and microchondrules are FeO-poor and have pyroxene-normative compositions (Fs6.2 Wo8.5 and Fs8.6 Wo0.2, correspondingly).

BK16 exhibits mineralogical evidences of sulphidization (corrosional replacement mainly of Fe,Ni grains by iron sulfide), oxidation (development of Fe-enriched rims on the edges of forsterite and perovskite grains, formation of iron hydroxides on the edges of Fe,Ni grains and on the interphase boundaries of silicates), and aqueous processing (formation of calcite and extensive development probably of Fe-phyllosilicates with a fibrous texture predominantly around metal grains).

It is suggested that the Krymka xenolith formed by the accretion of unequilibrated dusty material bearing significant abundance of high-temperature minerals (perovskite, spinel, forsterite, enstatite). After consolidation BK16 experienced low-temperature hydrothermal processing, which is typical for carbonaceous material. In addition terrestrial weathering of Krymka promoted to formation of iron hydroxides in the xenolith. SiO2/MgO-ratio, fine-grained texture, high modal abundance of metal, and mineralogical evidences of a aqueous processing allow to speculate that the xenolith BK16 represents a fragment of a probable primitive precursor of H-chondrites.

Acknowledgements: SEM and microanalytical data were obtained at the Institut für Planetologie, Münster, Germany. We thank A. Bischoff for a kind support of this study, and T. Grund, U. Heitmann, A. Sokol, and M. Niemeier for technical assistance.

References: [1] Semenenko V. P. et al. 2004. Geochim. Cosmochim. Acta 68:455-475. [2] Semenenko V. P. et al. 2005. Geochim. Cosmochim. Acta 69:2165-2182. [3] Semenenko V. P. and Girich A. L. 1999. Meteoritics & Planetary Science 34:A106. [4] Semenenko V. P. et al. 2001. Ibid. 36:1067-1085.


EXPOSURE HISTORIES OF THREE METEORITES FROM RIO CUARTO ARGENTINA. F. Serefiddin1, G. F. Herzog1, P.H. Schultz2 and L. Schultz3. 1Dept. of Chemistry and Chemical Biology, Rutgers University, Piscataway NJ 08854, USA, 2Brown University, Providence, RI 02912, 3Max-Planck-Institut für Che-mie, 6500 Mainz, Germany.

Introduction: A discovery in the Río Cuarto, Argentina area

of a meteorite with a large preatmospheric mass and the right ter-restrial age could help corroborate any link between certain mete-orites [1,2] found in or around elongate structures. Others have suggested that the meteorites might be the result of an atmospheric burst or simply finds [3]. Here we report measurements of cos-mogenic nuclides in 3 provisional meteorites, 2 found in, and 1 found adjacent to the East Twin Crater at Rio Cuarto.

Experimental methods: We used accelerator mass spectrome-try at PRIME Lab of Purdue University to measure the concentra-tions of 36Cl, 26Al, and 10Be in powdered whole rock samples [see 4]. Analyses of the light noble gases were carried out at the Max-Planck-Institut of Mainz following [5].

Results and discussion: Siderophile element abundances [6] and thin section data [1] for RC1-3 are consistent with their classi-fication as H-chondrites. The CRE age for RC3 falls on a well-defined peak for H chondrites around 7 My. The differences among the three exposure ages exclude pairing. If due only to GCR production, high cosmogenic 22Ne/21Ne ratios of ~1.24 in RC1 and RC2 imply preatmospheric depths of less than 2 cm and meteoroid sizes that were certainly less than 40 cm and probably less than 10 cm [7,8]. Assuming a terrestrial age <0.1 My, the relatively low 10Be and activities are also consistent with low shielding. If SCR irradiation raised the 26Al activities (and 22Ne/21Ne ratios) in RC1 & RC2, then the upper limit on size could be larger than 40 cm. In RC-3, the 22Ne/21Nec ratio of 1.15 indicates a preatmospheric depth of less than ~15 cm; 10Be of ~19 dpm/kg indicates a preatmos-pheric radius between ~ 20 and 65 cm. The 26Al activity of 46 dpm/kg is consistent with a wide range of irradiation conditions. We conclude that RC3 was too small in space to have produced a 100-m crater.

References: [1] Schultz P.H. and Lianza R.E. (1992) Nature 355, 234-236. [2] Schultz P.H. et al. (2004) EPSL 219, 221-238. [3] Bland P.A., et al. (2002) Science 296, 1109-1111. [4] Leya I. et al. (2001) M&PS, 36 1479-1494. [5] Scherer P. and Schultz L. (2000) M&PS 35, 145-153. [6] Koeberl C. and Schultz P.H. (1992) LPSC XXIII, 707-708. [7] Leya I. et al. (2000) M&PS 35, 259-286. [8] Masarik J. et al. (2001) M&PS 36, 643-650. [9] Eugster E. (1988) GCA 52, 1649-1659

Table 1. RC1 RC2 RC3 (22Ne/21Ne)c 1.25 1.25 1.15 Tavg (My) 12.2±1.4 3.5±0.4 8.0±0.2 10Be (dpm/kg) 13.7 11.8 19.0 26Al (dpm/kg) 57.6 53.5 45.6 Tavg, in My is average of 3He, 21Ne and 38Ar ages [9] as-suming H-chondrite composition; c=cosmogenic


MELT-VEIN CRYSTALLIZATION AS AN ALTERNATIVE MEANS OF CONSTRAINING SHOCK PRESSURES IN CHONDRITES. Thomas G. Sharp1, Zhidong Xie1, Paul Decarli2 1Geological Sciences Department, Arizona State University, Tempe, AZ 85287, U.S.A. [email protected], [email protected]. 2 SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025, paul.decarli@ sri.com

Introduction: A record of impact processes on meteorite

parent bodies is recorded as shock-metamorphic effects in mete-orites. These include brecciation, deformation, phase transforma-tions, local melting and subsequent crystallization [1]. The key to reading this record is to use the shock effects to estimate the pressure and duration of shock events, which can be used to con-strain velocities and sizes of the impacting bodies. Shock pres-sures have been estimated in natural samples by calibrating the pressures needed to generate specific deformation and transfor-mation effects in shock-recovery experiments [1]. An alternative to calibrating the pressures of phase transitions with shock-recovery experiments is to use the mineralogy of shock-induced melt that crystallizes at high pressure [2]. However, the mineral-ogy and textures expected for rapid quench at high pressure are not known, and crystallization assemblages may be metastable.

Samples and Methods: In order to use melt-vein mineralogy to constrain shock pressures, we have studied melt-vein assem-blages in a variety of shocked meteorites from shock stage S3 to S6. We are currently undertaking high-pressure quench experi-ments in the multi-anvil apparatus to investigate the crystalliza-tion assemblages and textures that result from rapid quench of a chondritic melt at high pressure. These experiments use a 8-mm MgO-Al2O3 octahedral pressure medium and a 3-mm truncated edge length (TEL) on WC cubes. The starting material used is crushed Mbale L6 chondrite in a graphite or Fe-Ir capsule. The sample is heated with a Re-foil furnace, while the temperature was monitored at pressure with a type-C thermocouple. So far, we have preformed experiments from 18 to 23 GPa and tempera-tures from 2200 to 2440 °C. Samples are quenched by cutting the power to the furnace, which results in a temperature drop to ~ 300 °C in ~ 1.5 seconds [3].

Results: So far, we have five successful super-liquidus quench runs from 18 to 23 GPa that contain majorite, ring-woodite and an acicular mineral that appears to be akimotoite. Control of quench rates has been problematic because of furnace failures at such high temperatures, but this problem has been solved. These experiments as well as new results will be dis-cussed and compared to the melt-vein quench textures and as-semblages seen in natural samples. The results of these quench experiments, along with available phase-equilibrium data are used to constrain crystallization pressures in natural samples.

References: [1] Stöffler D. et al. (1991) GCA,55, 3845-3867. [2] Chen M. et al. (1996) Science 271, 1570-1573.[3] Heinemann et al. (1997) Physics and Chemistry of Minerals 24, 206-221.


PETROGENETIC LINKAGES BETWEEN THE MG-SUITE AND OTHER EPISODES OF KREEP BASALTIC MAGMATISM. C.K. Shearer1, L. Borg1, and J.J. Papike 1. Insti-tute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, N. M. 87131, [email protected].

Introduction: The record of basaltic magmatism on the Moon indicates that lunar mantle melting and basalt transport to the lunar crust occurred over a period of at least 3.4 billion years from 4.46 Ga [1,2] to 1.0 Ga [3,4]. The production of KREEP-rich basalts appears to extend over a significant portion of this period from the emplacement of the Mg-suite (starting at 4.46 Ga) to basaltic magmas represented by olivine cumulate clasts in NWA773 at 2.928±0.034 Ga [5]. This KREEP geochemical signature probably represents the last dregs of residual liquid remaining from the crys-tallization of the lunar magma ocean (LMO). Isotopic ratios and ratios of incompatible trace elements of KREEP-rich rocks virtu-ally all conform to a single uniform pattern, suggesting that the KREEP component was derived from a single source. Here, we compare the geochemical and isotopic characteristics in the wide variety of KREEP-rich basaltic lithologies to explore: (1) the petro-logic relationships between the Mg-suite and other products of KREEP-rich basaltic magmatism and (2) the mechanisms by which the KREEP signature was incorporated into these basaltic magmas.

Results: Trace element characteristics in olivine are distinctly different among the lunar magmatic rocks. The Mg-suite litholo-gies are typified by silicates with relatively high Mg′, yet early liq-uidus phases such as olivine are fairly low in Ni. This contrasts with olivine in other lunar basalts. Although the Cr content of the mare basalts are distinctly different and higher than most terrestrial basalts, the Cr content in olivine from the Mg-suite indicates that these magmas have chromium contents similar to terrestrial basalts. Differences in Ni, Co, and Cr indicate that the “mafic component” in the KREEP-rich magmas varies in composition and suggests derivation from different mantle sources. The high Y and low Ti/Y in olivine indicates that the parental basaltic melts were also high in incompatible elements and contained the ilmenite fractionation signature identified with KREEP. Initial Sr isotopic compositions of the source regions for these KREEP-rich magmas range from a 87Rb/86Sr ratio of 0.07 for the relatively young NWA773 to 87Rb/86Sr ratios of 0.015 for the older Mg-suite lithologies.

Discussion: Although basaltic magmatism associated with KREEP extended for over 1.5 billion years, it appears that the style of this magmatism changed over time. The early stages of this magmatism (Mg-suite) seemed to represent melting of early lunar magma ocean cumulates. These mantle source regions had rela-tively low incompatible element enrichment. Later stages of KREEP-rich basaltic magmatism seemed to involve melting of a variety of LMO cumulate assemblages with higher incompatible element enrichment. These changes in characteristics in KREEP-rich basalts indicate that although there was, perhaps, a single KREEP component that was a product of extensive LMO crystalli-zation, different magmas incorporated this signature. It appears that the heat derived from the KREEP component was instrumental in at least initiating melting over this period of time. References: [1] Shih et al. (1993) GCA, 57, 915-931. [2] Nyquist and Shih (1992) GCA 56, 2213-2234. [3] Schultz and Spudis (1979) Proc. 10th LPSC, 2899-2918. [4] Hiesinger (2002) GRL 29, 10.29/2002GL 014847. [5] Borg et al. (2004) Nature 432, 209-211.



CHEMICAL CHARACTERISTICS OF NAKHLITE, MIL 03346. N. Shirai and M. Ebihara. Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Ha-chiouji, Tokyo 192-0397, Japan.

Introduction: MIL 03346 was a newly discovered nakhlite

from Miller Range on Antarctica in December 2003 [1] and is the 7th nakhlite in addition to Nakhla, Lafayette, Governador Val-adares, Y 000593, NWA 817 and NWA 998. Although nakhlites are mostly composed of augite, with olivine and mesostasis as minor phases, petrographic difference among nakhlites is re-vealed by the abundance of mesostasis. We determined major, minor and trace elements for their bulk compositions by PGA, INAA and ICP-MS. Based on analytical data, we aim to charac-terize MIL 03346 in chemical composition.

Result and discussion: Our data are in good agreement with literature values of MIL 03346 [2] for comparable elements. Mg/Si and Ca/Si ratios of MIL 03346 are 0.30 and 0.32, respec-tively, entering in the nakhlite area with Mg/Si ratio = 0.28-0.41 and Ca/Si ratio = 0.31-0.34 [3]. In comparison with other nakhlites, Na, Al, K and Ti abundances of MIL 03346 are similar with those of NWA 817 and are about two times higher than those of other nakhlites. Ba, REE, Hf, Th and U abundances of MIL 03346 also show a similar trend. Petrographic study shows that mesostasis abundances of MIL 03346 and NWA 817 are about two times higher than those of other nakhlites [4]. Thus, incompatible element abundances of MIL 03346 and NWA 817 are higher than those of other nakhlites. Chemical composition is consistent with mineral abundance.

CI chondrite-normalized REE abundance pattern of MIL 03346 is LREE-enriched (CI chondrite-normalized La/Lu = 4) and is similar to those of other nakhlites although REE abun-dances for MIL 03346 and NWA 817 are systematically higher than those for other nakhlites. In consideration of REE contents and their abundance pattern, MIL 03346 and NWA 817 were suggested to cumulate later in the basaltic melt source whose REE abundances were homogeneous.

In contrast with Earth and Moon rocks, Martian meteorites have characteristic Hf/Sm ratios; Hf/Sm ratio of shergottites are superchondritic while those of nakhlites and chassignite are sub-chondritic. As simple partial melting of bulk silicate Mars calcu-lated by [5] cannot explain Hf/Sm ratios of nakhlites and chas-signite, it can be postulated that the source materials for these Martian meteorites were supplied as an ascending plume from the deep region of Martian mantle where majorite and/or perovskite were partly melted, increasing Hf/Sm ratios in melt in accordance with their partition coefficients.

References [1] Antarctic Meteorite News Letter. 2004, 27 (2) [2] Anand M. et al. 2005. Abstract #1639. 36th Lunar & Planetary Science Conference. [3] Shirai N. and Ebihara M. 2005. Antarctic Meteorites Research 17: 55-67. [4] Treiman A. H. 2005. Chemie der Erde Geochemistry. 65, in press. [5] Longhi et al. 1992. Mars, 184-208.


NONDESTRUCTIVE 3D STRUCTURE AND MORPHOLOGY OF METEORITES. A. Simionovici1, L. Lemelle1, Ph. Gillet1, B. Zanda2, G. Libourel3, P. Bleuet4, 1LST – École Normale Supérieure de Lyon, 46 allée d’Italie, 69007 Lyon, FRANCE, 2LEME, Muséum National d'Histoire Naturelle, 57, rue Cuvier, 75005 Paris, FRANCE, 3CRPG, BP 20, 54501 Vandoeuvre-Les-Nancy, FRANCE, 4 ESRF, BP 220, 38043 Grenoble, FRANCE, E-mail: [email protected]

Introduction: When attempting to characterize unique and

fragile samples such as meteorites, non-destructive, non-invasive methods should be applied first, insuring subsequent analyses of destructive potential. When bulk quantitative information is re-quired with high spatial resolution the only method available without sample sectioning is the synchrotron X-ray coupled to-mographies, combining fluorescence and Compton spectrometry with tomography [1]. This recently perfected method allows the estimation of elemental concentration of elements of Z≥ 14 in the bulk of sub-millimeter meteoritic grains with micron precision, as well as an average Z imaging for the Z≤10 non-fluorescing elements composing the matrix.

Achondrites: In preparation for the Martian return samples this method was applied to search for extraterrestrial life traces by imaging fractures and aqueous alteration phases in the Mar-tian NWA 817 meteorite measured in conditions mimicking a quarantine [2]. This method has recently been extended to image full volumes with elemental capabilities by spiral scanning to-mography [3].

Chondrites: Recently, this method was applied to a millime-tre grain of the Semarkona LL3 chondrite in order to constrain the distribution of volatile elements such as Cu and Zn between chondrules and matrix, of great interest in the study of the origin of chondrules [5]. Using high resolution X-ray absorption tomo-graphy, the sample morphology recording the sizes and location of chondrules and CAIs can easily be measured and further treated using volume manipulation and metrology codes. These results can also direct ICPMS and TEM sample preparation strategies insuring access to chondrules or CAIs without risk. Examples of these analyses will be presented together with ongo-ing optimization strategies of this method.

References: [1] B. Golosio, A. Simionovici, A. Somogyi, L. Lemelle, M. Chukalina, A. Brunetti, 2003, Internal elemental microanalysis combining X-ray fluorescence, Compton and transmission tomography, Journal of Applied Physics 94, 145-157. [2] L. Lemelle, A. Simionovici, R. Truche, Ch. Rau, M. Chukalina, P. Gillet, 2004, A new nondestructive X-ray method for the determination of the 3D mineralogy at the µm-scale, American Mineralogist 87, 547-553. [3] B. Golosio, A. Somogyi, A. Simionovici, P. Bleuet, L. Lemelle, 2004, Nondestructive Quantitative 3D Elemental Microanalysis by Combined Helical X-ray Microtomographies, Applied Physics Letters 84, 2199-2201. [4] A. Simionovici, B. Golosio, M. Chukalina, A. Somo-gyi, L. Lemelle, 2004, 7 years of X-Ray Fluorescence Tomogra-phy, SPIE Vol. 5535, 232-242. [5] Hewins, R.H., Yu, Y., Zanda, B. and Bourot-Denise, M., 1997, Do nebular fractionations, evaporative losses, or both, influence chondrule compositions? Antarctical Meteoritic Research 10, 294-317.


REFRACTORY INCLUSIONS FROM THE CM2 CHONDRITE LEW85311. S. B. Simon1, C. G. Keaton2, and L. Grossman1,3.. 1Dept. Geophysical Sci., The University of Chicago, 5734 S. Ellis Ave., Chicago, IL 60637. E-mail: [email protected] 2Illinois Math and Science Academy, Aurora, IL 60506. 3The Enrico Fermi Inst., The Univ. of Chicago, Chicago, IL 60637.

Introduction: Freeze-thaw disaggregation, followed by den-

sity separation in heavy liquids and hand-picking under a binocular microscope, has proven to be an effective technique for recovery of refractory inclusions from CM chondrites [1]; yet, few meteorites have been studied this way. We applied this technique to Antarctic CM LEW85311 (LEW) to characterize its refractory inclusion population and to compare it to that of the well-studied Murchison. We selected this meteorite because, of the CMs large enough for this type of study, its bulk oxygen isotopic composition is the most 16O-rich, suggesting it is the least hydrothermally altered [2].

Methods: Following 31 freeze-thaw cycles, particles that sank in a methylene iodide-acetone solution were examined under a bin-ocular microscope. A suite of spherical and/or blue particles were mounted, polished, studied with a scanning electron microscope, and analyzed by electron probe.

Results: Of 42 particles examined thus far, 32 are chondrules, nine are hibonite-bearing inclusions and one is a hibonite crystal ~150 µm long. Eight are porous, spinel(sp)-hibonite(hib)-perovskite(pv)±melilite(mel) objects generally similar to many previously found in CMs. In contrast with disaggregated Murchi-son samples [1, 3], we have found no inclusions with phyllosilicate or Al-diopside rims, and none contain any Al-diopside, a phase common in Murchison and Mighei [1, 3, 4]. Three inclusions have additional unusual features. One is a sp-free, very compact, proba-bly sintered aggregate of hibonite grains that are ~40 µm long. Some have serrated boundaries, interlocking with adjacent grains. Most pv is interstitial to hib. In sharp contrast is an oval (300 x 400 µm), hollow inclusion (#R10). It is basically a shell of material with typical spherule mineralogy: hibonite blades in spinel with relatively coarse (~15µm) mel and blebby pv. Inclusion R11 is large (~400 µm in diameter), very porous, and zoned, with a spinel-dominated mantle and a hib-dominated core. In both R10 and R11 mel occurs in contact with hib. In R10 the contacts are diffuse. In R11, they are sharp and, in many places, mel mantles hib. As in Murchison, spinel V2O3 contents are positively correlated with V2O3 contents of coexisting hib, but TiO2 contents of coexisting hib and sp are not correlated. As in Murchison, mel is Åk0-15.

Discussion: Refractory inclusions from LEW exhibit some similarities and some differences with inclusions from Murchison and Mighei, and the differences could be quite important. In spinel-rich Murchison inclusions, mel is very rarely in contact with hi-bonite, and even more rarely mantles it. The unusual textures of R10 and R11 probably reflect incipient conversion of hibonite to mel, predicted by thermodynamic models but rarely seen in sam-ples. LEW may have sampled a higher proportion of inclusions in which the hibonite-to-mel reaction is recorded than Murchison. Such samples will help us understand the origin of mel-poor, hi-bonite-, spinel-rich inclusions.

References: [1] MacPherson G. J. et al. 1983. Geochimica et Cosmochimica Acta 47:823-839. [2] Clayton R. N. and Mayeda T. K. 1999. Geochimica et Cosmochimica Acta 63:2089-2104. [3] Simon S. B. and Grossman L. 2004. Chondrites and the Protoplanetary Disk. pp. 185-186. [4] MacPherson G. J. and Davis A. M. 1994. Geochimica et Cosmochimica Acta 58:5599-5625.



MELTING OF ALLENDE AT PRESSURES BETWEEN 1 AND 25 MPa. S. J. Singletary1, T. L. Grove2 and M. J. Drake1, 1Lunar and Planetary Labora-tory, University of Arizona, Tucson, AZ, 85721. 2Dept. Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA 02139 ([email protected], [email protected] [email protected]).

Introduction: The carbonaceous chondrite (CC) meteorites

are widely accepted as representing the most primitive material in the meteorite inventory. They contain abundances of non-gaseous elements similar to those of the solar photosphere [1] and are considered to approximate the composition of the primi-tive solar nebula. The compositions of the different CCs have been used in modeling and experimental studies to gain insight into the processes that occurred in the early solar nebula and to understand how the planetary bodies in the solar system came to acquire their unique compositional characteristics [2-6].

While previous investigations have contributed much to our knowledge of the igneous evolution of the early solar system, an important region of pressure-temperature space that would repro-duce the conditions expected on bodies greater than 10 km but less than 250 km in radius, remains unexplored - specifically pressures of 1 to 25 MPa and temperatures greater than 1000ºC. The presence of bodies 10 to 250 km in radius in the early solar system is implied from the existence of various meteorite types that have old ages and record igneous processing at such pres-sures. One such group, the ureilites, records the effects of smelt-ing – a process that is suppressed at pressures exceeding 25 MPa [7].

Results: We present new data from reconnaissance low pressure (1-25 MPa) melting experiments on the Allende CV3 meteorite. The experiments were designed to explore the melting behavior of primitive compositions on small bodies in the early solar system and to examine the effect of removal of that melt on the residue composition. We find that pressures as low as 5 MPa enhance volatile retention and, influence melt composition.

Low degree melts produced at pressures of 1-25 MPa on small bodies in the early solar system are therefore hypothesized to be enriched in K, Al, and Na. When these enriched melts are removed from the parent bodies, they may create a residue capa-ble of generating ureilites.

References: [1] Anders E. and Grevesse N. 1989. Geo-chimica et Cosmochimica Acta 53:197–224. [2] Ringwood A. E. 1966. Geochimica et Cosmochimica Acta 30:41-104. [3] Seitz M. G. and Kushiro I. 1974. Science 183:954-957. [4] Agee C. B. 1990. Nature 346:834-837. [5] Jurewicz A.G. et al. 1993. Geo-chimica et Cosmochimica Acta 57:2123-2139. [6] Agee C. B. et al. 1995. Journal of Geophysical Research 100:17725-17740. [7] Walker D. and Grove T. 1993. Meteoritics 28:629-636.




STATUS OF THE JAMES M. DuPONT METEORITE COLLECTION 1995 TO 2004. P.P. Sipiera1, K.J. Cole1, J.R. Schwade1 , G.A. Jerman2 and B.D. Dod3. 1Schmitt Meteorite Research Group, Harper College, Pala-tine, IL 60067 [email protected]. 2Metallurgical Diagnostic Facility, NASA Marshall Space Flight Center, Hunts-ville, AL 35812 USA. 3Dept. of Physics and Earth Sciences, Mercer University, Macon, GA 31207 USA.

Introduction: From the mid 1950’s until his death in 1991,

James M. DuPont of Watchung, New Jersey gradually amassed the world’s largest private collection of meteorites. His last (1991) catalogue represented over 1,000 recognized meteorites and numerous unclassified specimens. Shortly after his death in July, 1991, the Planetary Studies Foundation of Algonquin, Illi-nois was asked to organize and inventory his collection. As a result of this work it was determined that the total number of rec-ognized meteorites stood at 970, with an additional 45 unclassi-fied specimens [1]. In 1995, the Planetary Studies Foundation acquired the entire collection and proceeded to return it to active status by analyzing the unclassified meteorites and acquiring new specimens through purchases, trades, and field research. As a result of these efforts the collection has grown to over 1400 rec-ognized meteorites.

Acquisitions: The Planetary Studies Foundation decided to increase the collection by first contacting reputable meteorite dealers to make purchases or initiate trades for recognized mete-orites. Secondly, new specimens were acquired for research pur-poses directly from individuals working in the deserts of North Africa. A cooperative effort developed between Richard and Ro-land Pelisson (SaharaMet) which led to the classification of 78 meteorites from Algeria, Libya and Western Sahara [2]. The Planetary Studies Foundation was also presented with the oppor-tunity to conduct three expeditions to search for meteorites in Antarctica. These efforts recovered a total of 54 meteorites over three field seasons [3, 4, 5]. In addition, the unclassified meteor-ites from the original DuPont collection were examined and submitted for acceptance to the Meteoritical Society.

Summary: Ten years after its acquisition by the Planetary Studies Foundation, the James M. DuPont Meteorite Collection remains a viable resource for meteorite researchers as well as an educational tool for the general public. From May, 1998 through June, 2000 over 200 specimens from the DuPont Collection were displayed at the U.S. Space and Rocket Center in Huntsville, Alabama. The Planetary Studies Foundation is currently working on creating a virtual meteorite museum on its website: www.planets.org which will feature a photo and description of every meteorite in its collection. In addition, numerous research-ers have requested and received material from the collection for their specific studies. Cooperative research between various in-stitutions is encouraged and appreciated for classifying the most exciting specimens.

References: [1] Sipiera, P.P. et al. 1995. Meteoritics 30: 579. [2] Cole, K.J. et al. 2003. Meteoritics and Planetary Science 38:A71. [3] Sipiera, P.P. et al. 2000. Meteoritics & Planetary Science 35:A148-149. [4] Sipiera, P.P. et al. 2002. Meteoritics and Planetary Science 37:A131. [5] Sipiera, P.P. et al. 2002. Me-teoritics and Planetary Science 37:A132.


http://www.planets.org/

MOLDAVITES FROM THE CHEB BASIN, CZECH REPUBLIC. R. Skála1 and M. Čada2. 1Institute of Geology, Academy of Sci-ences of the Czech Republic, Rozvojová 135, CZ-16502 Praha 6, Czech Republic. E-mail: [email protected]. 2Minerály Čada, B. Němcové 386, CZ-351 01 Františkovy Lázně, Czech Republic.

Introduction: Moldavites were found in the Cheb Basin,

Western Bohemia, in 1993 and reported by Bouška et al. [1]. Skála and Čada [2] analyzed three moldavites found about 3 km NW of the place of original moldavite finds reported in [1]. Be-tween 1993 and 2005, by guess 1200-1500 individual moldavite pieces have been collected in the Cheb Basin on 6 different lo-calities in the area of about 12 × 20 km. This identifies local Ter-tiary and Quaternary sediments as the third most prominent source of central European tektites known next to the Southern-Bohemian and Western-Moravian sub-strewnfields.

Physical properties and chemical composition: The hith-erto largest moldavite from the Cheb Basin weighs 36 g and was found in the gravel pit near Dřenice. The weight distribution is uneven: more than half of the ~ 300 samples from Dřenice gravel pit (64 %) weigh between 1 and 4 grams. Bulk densities cluster around 2.331 and 2.371 g.cm-3. Colors were determined visually based on the scale defined in [3]. Bottle and olive green mol-davites prevail, no brown-colored pieces were found. All the moldavites found in the Cheb Basin represent the splash-form tektites; no other primary shapes were reported. The most com-mon shapes, neglecting the fragments, are ellipsoid and droplet; the rarest forms are dumbbell- or rod-shaped.

Chemical composition was measured for nine samples with a JEOL JXA-8200 SuperProbe WD/ED combined electron probe microanalyzer. Major element contents follow (in wt.%): SiO2: 77.4-84.3; TiO2: 0.15-0.47; Al2O3: 6.63-10.8; FeO 0.8-2.13; MnO: up to 0.22; MgO: 1.59-3.06; CaO: 2.16-4.99; BaO: up to 0.25; Na2O: 0.2-0.59; K2O: 2.17-3.77. Major element chemistry defines at least 2 distinct groups differing mutually mainly in the contents of TiO2, Al2O3, and alkalies.

Conclusions: The physical properties (e.g., color and weight distributions) studied indicate that the moldavites from the Cheb Basin are very similar to those from the Southern Bohemia. The microprobe study results significantly expand the compositional range previously reported for Cheb moldavites [1, 2]. The HCa/Mg types of moldavites are by far less rare as supposed in [4]. In addition a group of moldavites exhibiting a transitional composition between ‘normal’ and HCa/Mg types was identified. A considerable chemical variability among individual moldavites as well as among individual point analyses of the individual mol-davites studied was detected.

Acknowledgements. This work was funded by the grant of the Czech Science Foundation (GAČR) No. 205/05/2593 and falls within the research plan AV0 Z30130516 of the Institute of Ge-ology AS CR.

References: [1] Bouška V. et al. 1995. Bulletin of Czech Geological Survey 70:73-80. [2] Skála R. and Čada M. 2003. Acta Scientiarum Naturalium Musei Moraviae Occidentalis Tře-bíč 41:11-17. [3] Bouška V. and Povondra P. 1964. Geochimica et Cosmochimica Acta 28:783-791. [4] Delano J.W. et al. 1988. 2nd International Conference on Natural Glasses, Prague: 221-230.


INFLUENCE OF TITANIUM CONTENT ON CRYSTAL STRUCTURE OF IRON MONOSULFIDE. R. Skála1 and M. Drábek2. 1Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 135, CZ-16502 Praha 6, Czech Republic. E-mail: [email protected]. 2Czech Geo-logical Survey, Geologická 6, CZ-15200 Praha 5, Czech Repub-lic.

Introduction: In aubrites, in which otherwise lithophile ele-ments behave like siderophile ones due to strongly reducing con-ditions, titanium-rich monosulfides were found. In the Bustee clast, titanium-bearing troilite, being associated with osbornite, heideite and oldhamite, contains 17.2 to 25.2 wt % Ti. In the Bishopville aubrite, the content of titanium in troilite is reported to reach up to 5.7 wt % [1]. Such contents agree well with ex-perimental results of [2] which indicated that pyrrhotite dissolves at least 32 wt. % Ti at 800 ºC.

Samples and experimental: Chemical composition of iron monosulfides was measured in three aubrites (Aubres, Bustee and Norton County) in polished thin sections with a JEOL JXA-8200 SuperProbe electron probe microanalyzer. Synthetic sam-ples were prepared from weighed high-purity elements in evacu-ated and sealed silica glass tubes in horizontal tube furnaces. X-ray powder diffraction patterns of the resulting synthetic materi-als were collected with Philips X’Pert and Stoe STADI P diffrac-tometers. The powder data of these specimens were then com-pared with standard patterns in the ICDD PDF-2 database.

Results: Titanium content in iron monosulfide of the aubrites Aubres and Norton County attains up to 1.9 and 3.0 wt %, re-spectively. The highest measured Ti content in troilite of Bustee was 8.7 wt. % - considerably less than reported earlier [1] but still indicating ~ 15 mol. % substitution of Ti for Fe. XRD study of synthetic Fe1-xTixS compounds showed that already for x = 0.05 the crystal structure of stoichiometric iron monosulfide (troilite) changes to pyrrhotite-type structure. For x ≤ 0.1 the powder patterns indicate the presence of a different polytype than for x ≥ 0.2, however, the unambiguous identification of a polytype is not possible from the powder data. Such behavior is consistent with ordering of Ti atoms within FeS lattice; possibly some layers within the crystal structure are completely built up by titanium instead of iron.

Conclusions: Iron monosulfides in aubrites contain always some Ti. Titanium significantly influences the crystal structure of iron monosulfide in our experimental runs. With increasing tita-nium content the crystal structure changes from troilite-type for FeS to NiAs-type for TiS with intermediate members having various polytypic pyrrhotite-type structures. Consequently, it is questionable whether Ti-containing troilites reported from aubrites Bustee and Bishopville really correspond to troilite or rather titanium-bearing pyrrhotites.

Acknowledgements. This work was funded by the grant of the Czech Science Foundation (GAČR) No. 205/02/1101 and falls within the research plan AV0 Z30130516 of the Institute of Ge-ology AS CR.

References: [1] Mittlefehldt D.W. et al. 1998. Reviews in Mineralogy and Geochemistry 36:4-1-4-195. [2] Vieane W and Kullerud G. 1979. Carnegie Institution Washington Yearbook 70:297-299.


INVESTIGATING FINE-GRAINED CONSTITUENTS OF METEORITES USING FIB AND SEM-STEM. C. L. Smith1 and M. R. Lee2. 1Department of Mineralogy, The Natural History Museum, London, SW7 5BD, UK. 2Department of Geographical and Earth Sciences, The Gregory Building, University of Glas-gow, Glasgow, G12 8QQ, UK.

Introduction: The investigation of sub-micron scale, fine-

grained material in meteorites, is, by necessity usually carried out using Transmission Electron Microscopy (TEM). However, in-herent difficulties with this technique often make it very difficult, or impossible to study specific areas or phases within a meteor-itic sample. Additionally, the sample preparation required to produce electron transparent samples for TEM is highly destruc-tive, hence is often unsuitable for rare and precious meteoritic material. With advances in instrumentation, new avenues have opened up whereby sample preparation may be carried out using a Focused Ion Beam (FIB) instrument causing minimal damage and TEM itself can be carried out using a Scanning Electron Mi-croscope (SEM) fitted with the required transmitted electron detector (SEM-STEM). We have studied both terrestrial and extraterrestrial samples using a combination of FIB and SEM-STEM and here describe results from the Murchison CM2 chondrite demonstrating the power of these new techniques.

Method: The areas of interest in a polished thin section of Murchison were first coated with a thin layer of Au to prevent charging. The FIB sections were then cut as described in [1]. The thinned slices were removed ex situ and placed on a TEM grid. The grid was then loaded into the detector and placed into the FEG-SEM. Both bright field and dark field images are ob-tainable, dependent on detector setting. Dark field images can provide qualitative information as to composition of different phases, as electron scattering is partly dependent on mean atomic mass (analogous to back scattered electron imaging in standard SEM).

Results: The technique is very good for resolving mixtures of minerals at a sub-micron to nanometre scale. Not only can different mineral phases be identified qualitatively using bright filed and dark field imaging, qualitative chemical analyses may also be determined using EDS, with an activation area of only a few nanometres. Samples from Murchison matrix and chondrule fine-grained rims display readily resolvable, nanometre scale, silicate, phyllosilicate and sulphide phases. Pentlandite, tochilin-ite and crysotile have all been identified in our samples. Sul-phide abundance decreases from the matrix to areas adjacent to the chondrule within fine-grained rims.

Conclusion: FIB preparation is a major breakthrough in sample preparation for TEM, allowing site-specific sampling with relatively little damage to the sample. Although SEM-STEM is not intended as a replacement for traditional TEM it has many advantages. It is much cheaper (a few thousand dollars compared with a few hundred thousand dollars), and with rela-tively little training an experienced SEM user can readily obtain good results. Combining FIB and SEM-STEM has many poten-tial applications in meteorites. We are continuing our work inves-tigating other fine-grained meteorite components, for example, C-rich matrix in ureilites.

References: [1] Lee at al. 2003. Mineralogical Magazine 67:581-592.


MINERALOGY OF THE LUNAR METEORITES KALAHARI 008 AND KALAHARI 009. A. K. Sokol1 and A. Bischoff1. 1Institut für Planetologie, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany. E-mail: [email protected].

Introduction: In 1999, the first meteorites from Botswana

were recovered [1]. Two of these samples were found close to the small village of Kuke (Kalahari 008 and Kalahari 009) and are chemically and petrographically different lunar rocks. However, it is suggested that both samples represent distinct lithologies of one meteoroid that broke apart at the find site.

Results: During geological field work Kalahari 008 and 009 were found roughly 50 m apart in front of a small dune in Sep-tember 1999.

Kalahari 008 (598 g in weight) is an anorthositic breccia hav-ing typical clasts of lunar highland breccias (e.g., feldspathic crystalline melt breccias, granulitic lithologies, cataclastic anor-thosites etc.) embedded within a well-lithified matrix. An impact melt spherule indicates that this rock derives from the regolith. Olivine crystals are much less frequent and generally smaller than pyroxenes and display a distinct bimodal distribution in composition (~Fa42-66 and Fa78-98). Pyroxenes show a wide range of compositions (Fs14-77 Wo0.5-39 En8-76). Most plagioclases in clasts and matrix are anorthites (An92-99), typical of lunar high-land mineralogy.

Kalahari 009 is a single rock of about 13.5 kg. In texture and chemistry it differs from Kalahari 008. Considering bulk compo-sition and mineralogy Kalahari 009 can best be classified as a VLT lunar mare basalt. However, the rock is a breccia consisting of fragments of basaltic lithologies embedded in a fine-grained matrix. Many of the basaltic clasts have a coarse-grained subo-phitic texture. Clasts and matrix display the same composition. Pyroxene is the most abundant phase followed by plagioclase (mostly An86-96). Olivine (mostly Fa80-100) occurs less frequently.

Both samples are significantly shocked: all clasts are shocked to almost the same degree. Characteristic shock features include mosaicism and planar fracturing in feldspar and olivine (in both samples) as well as localized impact melting (within Kalahari 008). Partly, the transformation of plagioclase to maskelynite is visible in both samples. Such shock effects are typical for shock pressures of at least 15 – 20 GPa according to the calibration scheme of Stöffler et al. [2] for ordinary chondrites (S4).

Kalahari 008 clearly is an anorthositic breccia from the lunar highlands. Preliminary results of geochemical studies of Kalahari 009 (Zr/Hf = 30.2 and Nb/Ta = 17.4; C. Münker, pers. communi-cation) are typical for lunar rocks.

Conclusions: Although Kalahari 008 and 009 represent different rock types (anorthositic breccia vs. basaltic breccia) it is suggested that they belong to one meteorite fall. It would be very surprising to find two individual lunar meteorites this close to each other. Kalahari 008 contains a distinct population of Fa-rich olivine clasts (Fa78-98). These olivines are similar in composition to olivine in Kalahari 009. This may indicate that the Kalahari 008 breccia was formed in close vicinity to the Kalahari 009 basalt, and that both textural different rock types were ejected from the Moon as one polymict meteoroid.

References [1] Sokol A. K. and Bischoff A. (2005) Meteorit-ics & Planetary Science (submitted). [2] Stöffler D. et al. (1988) Geochim. Cosmochim. Acta 55:3845-3867.


26AL-26MG CHRONOLOGY OF THE D’ORBIGNY AND SAHARA 99555 ANGRITES. L. Spivak-Birndorf1, M. Wad-hwa1, and P. E. Janney1, 1Isotope Geochemistry Laboratory, De-partment of Geology, The Field Museum, 1400 S. Lake Shore Dr., Chicago, IL 60605. E-mail: [email protected].

Introduction: The decay of the short-lived radionuclide 26Al (t1/2 ~0.72 My) has been applied extensively as a fine scale chro-nometer for dating early solar system events. However, definitive evidence for the in situ decay of 26Al, inferred from excesses of its daughter isotope, 26Mg, has only been reported in a small number of differentiated meteorites [1-3]. As part of our investi-gation of 26Al-26Mg systematics in achondrites, we report here the results of Mg isotopic analyses of several angrites.

Results and Discussion: We have measured high-precision Mg isotopic compositions of bulk rock samples and various min-eral separates of D’Orbigny (olivine, pyroxene and plagioclase), Sahara 99555 (pyroxene and plagioclase) and NWA 1670 (oli-vine and pyroxene) by MC-ICP-MS. The Mg isotopic composi-tions of bulk rocks and mineral separates of these three angrites vary by up to 0.2 ‰ amu-1 relative to the Mg isotopic standard DSM3. Within uncertainties, all the samples fall along a mass-dependent fractionation line defined by a variety of terrestrial materials analyzed in our laboratory, with the exception of pla-gioclase separates from D’Orbigny and Sahara 99555, which have resolvable excesses of 26Mg from the decay of 26Al. Mineral separates and bulk rocks of D’Orbigny and Sahara 99555 define 26Al-26Mg isochrons corresponding to 26Al/27Al ratios of (5.1 ± 0.3) × 10-7 and (4.1 ± 1.2) × 10-7, respectively, at the time of their last equilibration. Relative to the Efremovka CAI E60 that has a 26Al/27Al ratio of (4.63 ± 0.44) × 10-5 and a Pb-Pb age of 4567.4 ± 1.1 Ma [4], we calculate 26Al-26Mg ages of 4562.7 ± 1.1 Ma and 4562.5 ± 1.2 Ma for D’Orbigny and Sahara 99555, respec-tively.

Evidence for the former presence of live 53Mn has been re-ported in D’Orbigny and Sahara 99555 [2, 5]. The weighted av-erage of the 53Mn/55Mn ratios determined for D’Orbigny by [2, 5] is (3.23 ± 0.04) × 10-6; Sahara 99555 is inferred to have a similar 53Mn/55Mn ratio [2]. Comparison with the LEW86010 angrite, which has a 53Mn/55Mn ratio of (1.34±0.05) × 10-6 (calculated as the weighted average of the 53Mn/55Mn ratios determined for this sample by [6, 7]) at 4557.8 ± 0.5 Ma [8], results in a 53Mn-53Cr age of 4562.5 ± 0.5 Ma for D’Orbigny. This is in excellent agreement with the 26Al-26Mg age estimated by us for this mete-orite. Furthermore, a recent reevaluation of the Pb-Pb data for D’Orbigny by Jagoutz and colleagues has resulted in an age of 4563 ± 1 Ma for this sample (G. W. Lugmair, pers. comm.), indi-cating that the 26Al-26Mg, 53Mn-53Cr, and Pb-Pb chronometers are indeed concordant in D’Orbigny.

References: [1] Srinivasan G. et al. 1999. Science 284: 1348. [2] Nyquist L. E. et al. 2003. Abstract #1388. 34th Lunar and Planetary Science Conference. [3] Wadhwa M. et al. 2004. Ab-stract #1843. 35th Lunar and Planetary Science Conference. [4] Amelin Y. et al. 2002. Science 297: 1678. [5] Glavin D. P. et al. 2004. Meteoritics and Planetary Science 39: 693. [6] Nyquist L. E. et al. 1994. Meteoritics 29: 872. [7] Lugmair G. W. and Shu-kolyukov A. 1998. Geochimica et Cosmochimica Acta 62: 2863. [8] Lugmair G. W. and Galer S. J. G. 1992. Geochimica et Cos-mochimica Acta 56: 1673.


SHOCK-GENERATED MELT NETWORKS IN ANORTHOSITIC TARGET ROCKS FROM THE MANICOUAGAN IMPACT STRUCTURE. J.G. Spray and E.L. Walton, Planetary and Space Science Centre, Department of Geology, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick, E3B 5A3, Canada ([email protected])

Introduction: We report field-based, petrographic and analytical electron microscopic investigations of target anorthositic rocks located beneath the melt sheet of the ~100 km diameter, 214 Ma Manicouagan impact structure of Quebec, Canada [1, 2]. Within the central uplift on Île René Levasseur, along the shores of Memory Bay, excellent exposure of the melt sheet-footwall contact occurs. Unusual localized melt textures in anorthosite are developed within 50 m of the contact.

Field observations: The texture is represented by the sporadic development of a network of melt veins associated with in situ brecciation. These form a 3-D interlinked honeycomb framework that pervades the host rock in sheets that range in thickness from tens of cm to several metres. The sheets are laterally extensive and generally subhorizontal. Individual honeycombs are typically equidimensional with diameters of 1-10 cm.

Microscopic observations: Within 50 m of the overlying melt sheet the anorthosites (plagioclase + opx + cpx + garnet) exhibit strong maskelynitization [3, 4]. The melt component is now present as glassy veins and pockets, which locally show quench crystallization and/or partial devitrification. Some are retrogressed to secondary phases (e.g., prehnite). Typical thicknesses for the melt networks, which define the honeycomb framework, are 2-5 mm, with local concentrations at honeycomb intersections reaching up to 10 mm width. New crystallites of hyalophane have been found in some of the networks (10-12 weight % celsian component). Clasts of host rock material also occur within the melt networks. Some of the thicker glassy networks exhibit schlieren fabrics. Field and microscopic evidence favours the networks being formed in situ, not as introduced melts from an extraneous source.

Origins: We reject thermal metamorphism and anatexis from the overlying, originally superheated, melt sheet as the cause of melt network generation. This is because the intensity and distribution of the networks cannot be equated with position relative to the overlying melt sheet. Also, the networks are closely associated with in situ brecciation. Instead, we interpret the melt networks as being shock-related. Brecciation and melting associated with the passage of the shock wave, followed by rarefaction and decompression, are considered the prime energy sources.

Implications: We draw parallels with shock veins and melt pockets developed in the more highly shocked meteorites (including lunar and martian samples) [5]. Melt pockets in meteorites have few if any known terrestrial equivalents, so the Manicouagan examples may be important links that enable us to place the development of this type of shock response in a spatial context within an impact structure. This may enable us to relate the lofting site of meteoroids to favourable launch positions within source craters on other planetary bodies.

References: [1] Floran, R.J. et al. (1978) JGR, 83, 2737-2759. [2] Dressler, B.O. (1990) Tectonophys. 171, 229-245. [3] Arndt et al. (1982) Phys. Chem. Min. 8, 230-239. [4] White, J.C. (1993) Contrib. Mineral Petrol. 113, 524-532. [5] Walton E.L. et al. (in press) Geochim. Cosmochim. Acta.


AUGER SPECTROSCOPY AS A COMPLEMENT TO NANOSIMS STUDIES OF PRESOLAR MATERIALS. F. J. Stadermann1, C. Floss1, E. Zinner1, A. Nguyen1, and A. S. Lea2. 1Laboratory for Space Sciences, Washington University, St. Louis, MO 63130, USA. E-mail: [email protected]. 2Pacific Northwest Na-tional Laboratory, Richland, WA 99352, USA.

The NanoSIMS ion microprobe has proven to be an ideal tool

for locating isotopically distinct circumstellar materials on a sub-micrometer scale in a variety of extraterrestrial materials [e.g., 1-4]. However, to completely characterize presolar phases it is essen-tial to obtain chemical and mineralogical data beyond what the NanoSIMS can provide. Although this can be done in some cases with the transmission electron microscope (TEM), not all samples lend themselves to this analytical approach. Detailed investigations of the suitability of various analytical techniques have convinced us that scanning Auger spectrometry best complements the NanoSIMS by providing mineralogical information on a compara-ble spatial scale without the need for extensive sample preparation.

Auger spectroscopy is an electron beam technique that can be used for elemental imaging in a similar way as energy dispersive X-ray (EDX) analysis. The fundamental difference between EDX and Auger measurements lies in the size and location of the ana-lytical volume from which elemental information is extracted. While the spatial resolution of EDX is around 1 µm, Auger spec-troscopy can resolve elemental variations on a scale of tens of nm, which is more than sufficient for circumstellar oxide and silicate grains which are typically 200 – 500 nm in diameter [1].

We used Auger spectroscopy on several samples of interplane-tary dust particles (IDPs) and primitive meteorites that had previ-ously been searched for presolar phases with the NanoSIMS [5-7]. The NanoSIMS analysis areas were readily found with the Auger instrument, and by overlaying the (NanoSIMS) isotopic and (Au-ger) elemental raster images it was possible to positively locate the isotopically anomalous presolar phases in the high-resolution Au-ger images. In most cases, the presolar oxides and silicates could be recognized as elementally and/or structurally distinct grains within the sample matrix. Individual presolar grains were identified as SiC, corundum, hibonite, Mg-silicate or Fe-silicate [8], based on their C, O, Mg, Al, Si, Fe, Ca Auger signals. In some cases tenta-tive initial classifications, based on NanoSIMS secondary ion in-tensities, had to be corrected. Detailed information about the iso-topic and mineralogical compositions of presolar grains is impor-tant for providing clues about stellar nucleosynthesis and galactic chemical evolution, as well as about grain survival in the interstel-lar medium and in different solar system reservoirs.

Since the Auger measurements are non-destructive and can be done directly on the NanoSIMS sample mounts, Auger characteri-zations can be used routinely after (or between) isotopic measure-ments in the NanoSIMS. We plan to extend this multi-technique approach for further studies of presolar phases in meteorites, mi-crometeorites and IDPs.

References: [1] Nguyen A. N. and Zinner E. (2004) Science 303, 1496-1499. [2] Floss C. et al. (2004) Science 303, 1355-1358. [3] Messenger S. et al. (2003) Science 300, 105-108. [4] Moste-faoui S. and Hoppe P. (2004) Ap.J. 613, L149-L152. [5] Floss C. and Stadermann F. J. (2005) LPSC XXXVI, Abstract #1390. [6] Nguyen A. N. et al. (2005) this volume. [7] Floss C. and Sta-dermann F. J. (2004) LPSC XXXV, Abstract #1281. [8] Floss C. et al. (2005) this volume.


TOF-SIMS, NANOSIMS, AND TEM ANALYSIS OF ANHYDROUS CLUSTER IDPs. T. Stephan,1 P. Hoppe,2 and I. Weber1. 1Institut für Planetologie, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany. E-mail: [email protected]. 2Max-Planck-Institut für Chemie, P.O. Box 3060, 55020 Mainz, Germany.

Introduction: Anhydrous interplanetary dust particles

(IDPs) represent probably the most primitive solar system mate-rial available for laboratory analysis. Due to their high porosity, they are extremely fragile and have the tendency to break apart. Therefore, they are often found as so-called cluster IDPs, parti-cles that disintegrate into numerous fragments upon collection in the stratosphere. Several cluster IDPs were identified as carriers of presolar silicates [1], corroborating their primitive nature.

In continuation of our previous study [2, 3], we selected two new cluster IDP fragments for TOF-SIMS, NanoSIMS, and TEM analysis in order to further characterize primitive IDPs and pos-sibly their presolar inventory. The selected analytical techniques allow obtaining information on chemical, isotopic, and minera-logical properties of the samples on a sub-micrometer scale.

Samples and Experimental Procedures: Samples investi-gated in this study are fragments O2 from cluster L2021#5 and AM4 from cluster L2005#18. Both samples were hexane-rinsed, embedded in epoxy, and ultra-microtomed. Residual epoxy stubs, after slicing approximately one half of the respective particle, were used for TOF-SIMS, while sections were selected for NanoSIMS and TEM investigations [2].

Results and Discussion: TOF-SIMS and TEM studies show grain sizes lower than 1 µm within these very heterogeneous samples. Chemical analysis by TOF-SIMS yield CI-like bulk concentrations for most elements (Fig. 1). L2021#5 O2 is domi-nated by Mg-rich olivine and pyroxene, Fe-sulfide, and feldspar, L2005#18 AM4 by olivine, pyroxene, and some Fe-oxide (wüstite). These differences indicate that AM4 was formed under more oxidizing conditions than O2. Both samples are C-rich. Also alkali enrichments are observed for both samples. Na in AM4 is clearly associated with Cl that appeared in a ring-shaped distribution surrounding the particle section. Such surface corre-lated halogens are usually attributed to contamination [4, 5].

Outlook: Isotope data from ongoing NanoSIMS investiga-tion will be presented at the meeting.

Li C O Na Mg Al Si K Ca Sc Ti V Cr Mn Fe Co Ni Cu Rb Sr10-1

100

101

102 Li C O Na Mg Al Si K Ca Sc Ti V Cr Mn Fe Co Ni Cu Rb Sr

L2021#5 O2 L2005#18 AM4

A

bund

ance

/ C

I (M

g=1)

Fig. 1. Element ratios relative to Mg and normalized to CI.

References: [1] Messenger S. et al. 2003. Science 300:105–108. [2] Stephan T. et al. 2005. Abstract #1645. 36th Lunar & Planetary Science Conference. [3] Hoppe P. et al. 2005. Abstract #1301. 36th Lunar & Planetary Science Conference. [4] Stephan T. et al. 1994. 25th Lunar & Planetary Science Conference. pp. 1341–1342. [5] Rost D. et al. 1999. Meteoritics & Planetary Sci-ence 34:A99.


SHOCK RECOVERY EXPERIMENTS CONFIRM THE POSSIBILITY OF TRANSFERRING VIABLE MICRO-ORGANISMS FROM MARS TO EARTH. D. Stöffler1, C. Meyer1, J. Fritz1, G. Horneck2, R. Möller2, C. S. Cockell3, J. P. de Vera4, and U. Hornemann5. 1Humboldt-University at Berlin. E-mail: [email protected]. 2DLR, Institute for Aerospace Medicine, Köln. 3Open University, Milton Keynes, UK, 4Institute of Botany, Heinrich-Heine-University Düsseldorf, 5Ernst-Mach-Institute, Freiburg i.Br.

Introduction: With regard to the impact and ejection phase

we tested the case for the transfer of microorganisms from Mars to Earth. Using a high explosive set-up thin layers of bacterial endospores of Bacillus subtilis, of the lichen Xanthoria elegans and of the cyanobacterium Chroococcidiopsis sp. embedded be-tween two plates of gabbro were subjected to 10, 20, 30, 40 and 50 GPa which is the pressure range observed in Martian meteor-ites [1]. The actual shock pressure was determined from refrac-tive index measurements of the shocked plagioclase based on calibration data from [2]. Shock and post-shock temperatures were calculated on the basis of data in [3] and [1]. The survival rates of the microbes were quantitatively determined using vari-ous biological and microscopic methods [e.g., 4].

Results: The bacterial endospores, the lichen and the cyano-bacterium do survive in the shock pressure range observed in Martian meteorites although the survival rates are exponentially decreasing with increasing shock pressure. The symbiotic sub-systems of lichen display different survival rates: The mycobi-onts survive up to 50 GPa at a rate of 0.002 % whereas the photobionts only reach a upper pressure limit of 31 GPa with a survival rate of 0.18 %. The endospores of Bacillus subt. survive up to 42 GPa with a rate of 0.02 %. Chroococcidiopsis sp. sur-vived only at 10 GPa with a rate of 0.39 %. The results are sur-prising in view of the relatively high shock and post-shock tem-peratures calculated for the applied pressures in gabbro. The temperature increase after shock compression at 20 °C increases from ~5 °C to 110 °C, 470 °C, and 760 °C at 10, 31, 42 and 50 GPa, respectively.

Conclusions: Our studies revealed different degrees of shock metamophism for the different petrographic types of Martian me-teorites [1]: 5 to 20 GPa for the nakhlites, 26 to 33 GPa for chas-signite, and orthopyroxenite, and 20 to 55 GPa for the shergot-tites. Although Bacillus subt. and the Xanthoria elegans are actu-ally capable of surviving in all types of Martian host rocks, the most favorable and most sufficient host rocks for the transfer of life from Mars to Earth are ultramafic rocks such as pyroxenites (nakhlites) which not only display the lowest degree of shock but also suffer the least from post-shock heating.

References: [1] Fritz, J. et al. 2005. Meteoritics & Planetary Science, in press. [2] Stöffler D. et al. 1986. Geochim. Cosmo-chim. Acta 50:889-903. [3] Artemieva, N. A. and Ivanov, B. A. 2004. Icarus 171:84-101. [4] Horneck G. et al. 2001. Icarus 149:285-293.


THE ORIGIN OF IMPACTORS DURING THE INNER SOLAR SYSTEM CATACLYSM. R. G. Strom1 , R. Malhotra1, T. Ito2, F. Yoshida2, and D. A. Kring1. 1Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 USA. E-mail: [email protected]. 2National Astronomical Observatory, Osawa, Mitaka, Tokyo 181-8588 Japan.

Introduction: The concept of a lunar cataclysm ~4 Ga is the

product of Ar-Ar, U-Pb, and Rb-Sr analyses of Apollo-era sam-ples [1,2], which suggest an intense bombardment ≤200 Ma long. More recent analyses of additional Apollo, Luna, and lunar me-teorite samples are consistent with the hypothesis [e.g., 3,4] and impact-reset ages among meteoritic fragments of asteroids and Mars suggest the cataclysm affected the entire inner solar system [5,6]. The source of the impacting debris has been controversial, although chemical fingerprints of impactors in lunar impact melts suggest asteroids were the dominant source [6].

Ancient Cratered Highlands: The impactors needed to cre-ate the ancient cratered highlands have a size distribution virtu-ally identical to the size distribution observed among main belt asteroids. This confirms asteroids dominated the flux of objects involved in the cataclysm, unless comets or Kuiper belt objects have the same size distribution. It also indicates the size distribu-tion of the main belt asteroids has not changed significantly since the cataclysmic bombardment ceased ~3.85 Ga. Furthermore, it indicates that the mechanism for the influx of asteroids operated in a size-independent fashion. Thus, the data point to mecha-nisms like the sweeping of resonances through the asteroid belt as the orbits of outer solar system planets changed. This type of orbital migration can produce a flurry of impacting asteroids over time scales of a few tens of millions of years, consistent with the geochronologic limits derived from impact melts; i.e., there truly was a cataclysmic spike in the impact rate, rather than a long, drawn out period of impact events over 500-700 Ma.

Post-cataclysm Impactors: The size distribution of impact craters on younger surfaces differs from that in ancient cratered highlands. The impactors needed to create craters on younger planetary surfaces have a size distribution similar to that of near-Earth asteroids (NEA), which have relatively more small objects than main belt asteroids. This indicates the delivery of asteroids from ~3.85 Ga through today has been influenced by a size-dependent process, such as the Yarkovsky effect.

Additional Implications: The absolute ages of inner solar system surfaces older than ~3.9-4.0 Ga cannot be reliably deter-mined from the cratering record because that record is dominated by the cataclysm. Younger inner solar system surfaces can be dated using the NEA impact flux. Impact cratering in the outer solar system probably involves a different flux of impactors and, thus, planetary surfaces in that region cannot be accurately dated with a lunar- or NEA-calibrated time scale.

References: [1] Turner G. et al. 1973. 4th Lunar Science Conference, pp. 1889-1914. [2] Tera F. et al. 1974. Earth & Planetary Science Letters 22:1-21. [3] Dalrymple G. B. and Ry-der G. (1996) Journal of Geophysical Research 101:26,069-26,084. [4] Cohen B. A. et al. 2000. Science 290:1754-1756. [5] Bogard D. D. 1995. Meteoritics 30:244-268. [6] Kring D.A. and Cohen B.A. 2002. Journal of Geophysical Research 107:4-1,4-6.


MICROSTRUCTURE OF A PRESOLAR HIBONITE GRAIN. R. M. Stroud1, L. R. Nittler2, C. M. O’D. Alexander2, F.J. Stadermann3, and E.K. Zinner3. 1Code 6361, Naval Research Laboratory, Washington, DC 20375, E-mail: [email protected]. 2Dept. of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015. 3Laboratory for Space Sciences and Physics Department, Washington Univer-sity, St. Louis, MO 63130.

Introduction: Thermodynamic equilibrium calculations of

dust condensation in oxygen-rich stellar outflows predict that corundum (Al2O3) is the first phase to condense, followed by hi-bonite (CaAl12O19) [1]. Microstructural studies of presolar grains provide the possibility to test these predictions, and help con-strain circumstellar condensation conditions. For Al2O3, the available structural data from two grains support the thermody-namic models [2], but no data from CaAl12O19 grains have been available. Comparison of the range of oxygen isotope values of the approximately 20 known presolar CaAl12O19 grains to those of the several hundred Al2O3 grains indicates that the two grain populations sample similar stellar source populations [3], and thus likely similar circumstellar condensation conditions. We report herein the first structural data from a presolar CaAl12O19 grain and confirm the structural phase identification as hibonite.

Methods: The hibonite grain was prepared as an acid resi-due of the Krymka ordinary unequilibrated chondrite (LL3.1) [3]. It was identified as presolar based on oxygen isotope measure-ments made with the Cameca ims 6f at the Carnegie Institution of Washington, and the identification was confirmed by measure-ments made with the Washington University NanoSIMS. We used the Nova 600 Dual Beam focused ion beam (FIB) work-station at the Naval Research Laboratory to prepare a thin section (200 nm x 150 nm across x 100 nm thick) of the 1-µm grain, which we characterized using a JEOL 2200FS transmission elec-tron microscope (TEM) equipped with a Noran Vantage energy dispersive x-ray spectroscopy (EDS) system.

Results: The oxygen isotope data (δ17O = 900, δ18O = -300) indicate that the grain belongs to Group 1, i.e, it originated in an O-rich asymptotic giant branch (AGB) star, with a mass ap-proximately 1.5 M and 0.9 x solar metallicity. Electron diffrac-tion patterns obtained from the [10 4 -3] and [10 11 1] zones con-firm that the grain has the hexagonal hibonite crystal structure. Some of the primary diffraction spots exhibit satellite spots, which indicate that the crystal is twinned. The grain composition determined by EDS using default k-factors is within experimen-tal error (3%) of stoichiometric CaAl12O19. The thin section shows no evidence for subgrains, but we cannot rule out the pos-sibility of subgrains in the remainder of the hibonite grain.

Discussion: Our measurements confirm that well-crystallized hibonite condenses in the outflows of O-rich AGB stars, in agreement with equilibrium thermodynamic calculations. Our results suggest that hibonite may contribute to features in the infrared spectra of some O-rich AGB stars. Analyses of addi-tional grains are planned in order to address the compositional range of presolar hibonite and any relationship to pre-existing Al2O3 grains or other possible subgrains.

References: [1] Lodders K. 2003. Astrophysical Journal 591:1220–1247. [2] Stroud R. M. et al. 2004. Science 304:1455-1457. [3] Nittler L. R. et al. 2005. Abstract #2200. 36th Lunar & Planetary Science Conference.


60FE-60NI SYSTEMATICS OF SOME ACHONDRITES N.Sugiura1 and Q. -Z Yin2. 1Univ. of Tokyo. E-mail [email protected]. 2Univ. of California at Davis.

Introduction: 60Fe is mainly produced by supernovae and not produced efficiently in AGB or by cosmic rays. Therefore, this is a crucial isotope to decipher the origin of extinct nuclides. Detection of significant excesses in 60Ni has been reported for several meteoritic samples [1,2,3], whereas significant excesses in 60Ni were not detected in other materials [4,5]. The upper limit to the initial 60Fe/56Fe of [5] is in conflict with some of the re-ported initial 60Fe/56Fe ratios [e.g. 3]. Here we report inferred initial 60Fe/56Fe ratios for old achondrites that contain minerals with high Fe/Ni ratios and hence can provide precise age data.

Ion probe measurements Iron-rich minerals in eucrites (Stannern and Asuka 881394: St and A88 for short) and angrites (Sahara 99555, D’Orbigny, Northwest Africa 1670 and Angra dos Reis: S99, D’O, NWA16 and ADOR for short) were meas-ured with a Cameca-6f ion microprobe. Fe/Ni ratios of minerals in ADOR were not high enough for chronological purposes and its data are not included in the following results.

Of the 3 Ni isotopes (60Ni, 61Ni and 62Ni) usually measured for Fe-Ni chronology, the abundance of 61Ni is the smallest and cannot be measured precisely. Hence we measured only 60Ni and 62Ni for this study. The error due to changes in the instrumental mass fractionation was estimated from repeated measurements of 60Ni/62Ni for a running standard sample. Other measurement pro-cedures are similar to those described in [4]. Corrections were made for tails of adjacent 44CaO and 46TiO peaks. A relative sen-sitivity factor of (Ni+/Fe+)/(Ni/Fe) ~0.75 was used for both Fe-rich olivine and pyroxene. This is similar to those used in [3, 4].

Results: Our preliminary results showed that all the 60Ni/62Ni ratios were normal within 2 sigma error. The inferred initial 60Fe/56Fe and 2 sigma error for St, A88, S99, D’O and NWA16 were (0.4±1.8) E-8, (-1.7±2.8) E-8, (-0.5±1.7) E-8, (3.0±3.5) E-8 and (3.2±3.5) E-8, respectively. S99, D’O and NWA16 have identical Mn-Cr ages and are about 5.1 Ma younger than CAIs. If data for these 3 angrites are combined, the initial ratio and the error are (0.6±1.4) E-8. According to Al-Mg systematics, A88 is about 3.9 Ma younger than CAIs. Using the age information, so-lar system initial 60Fe/56Fe ratios (at the time of CAI formation) were calculated to be (0.7±1.5) E-7 from combined angrites and (-1.0±1.7) E-7 from A88. St’s data did not yield useful limits to the initial ratio for the solar system.

Discussion: The small (upper limit) initial 60Fe/56Fe ratios found in the present study are consistent with those reported ear-lier for eucrites [e.g. 1]. But, the variation of the initial ratios within a eucrite [1] suggested that it may be disturbed after the solidification. In contrast, A88 and angrites studied here are pris-tine samples not affected by impacts. Their ages have been well determined by Al-Mg and/or Mn-Cr systematics. Therefore, the present results place strict limits to the solar system initial ratio of 60Fe/56Fe <2.2 E-7. This is smaller than the previous upper limit of [5] and in conflict with reported initial ratios of >5 E-7.

References: [1] Shukolyukov A. and Lugmair G.W. 1993. Sci. 259:1138-1142. [2] Tachibana S. and Huss G.R. 2003. As-trophys. J. 588:L41-L44. [3] Tachibana et al., 2005. Abs #1529. 34th Lunar Planet. Sci. Conf. [4] Kita N.T. et al., 1998. Antarc. Met. Res. 11:103-121. [5] Kita N.T. et al., 2000. Geochim. Cos-mochim. Acta 54: 3913-3922.


RECENT PROGRESS IN THE MODELING OF CORE-COLLAPSE SUPERNOVAE. F. D. Swesty. Department of Physics and Astronomy, SUNY at Stony Brook, Stony Brook, NY 11794-3800, USA. E-mail: [email protected].

It has been widely recognized for some time that core-collapse supernovae (explosions of massive stars) are one of the major engines for galactic chemical evolution. Despite this rec-ognition, however, we still do not understand the mechanism whereby the collapse of the core of a massive star turns into the violent explosion we observe. New calculations of the core-collapse event are providing new insight into the explosion mechanism [1]. These calculations employ two-dimensions and the multi-group-flux-limited-diffusion approximation for neu-trino transport. Future calculations will use eventually use full Boltzmann transport [2]. References: [1] Swesty F. D. and Myra E. 2005. in preparation. [2] Mezzacappa A. and Bruenn S. 1993. Astrophys. J. 405: 669–684.


PETROLOGICAL AND Ar-Ar STUDIES OF SHOCKED CHONDRITES. T. D. Swindle1, D. A. Kring1, J. Bond1, E. Ol-son1, and C. Jones2. 1Lunar and Planetary Lab, U. of Arizona, Tucson AZ. E-mail: [email protected]. 2U. of Pennsyl-vania, Philadelphia PA.

Although impact cratering and collisional disruption are the

dominant geologic processes affecting asteroids, very little is really known about them. We began studying these processes with the Cat Mountain L5 impact melt breccia [1] and have con-tinued with an investigation of the H chondrites Portales Val-ley[2], Ourique [3], and Orvinio [4]. Although a number of shocked L chondrites have been studied, shocked LL and H chondrites are less common, so studies of them have been less common as well. Based on limited data, [5] suggested the “lunar cataclysm” bombardment occurred over a much more extended period of time in the asteroid belt (until perhaps 3.4 Ga) than in the Earth-Moon system (~3.85 Ga). It is clear that more meteor-ite impact melts need to be studied and their ages determined to see if they really do record an event beginning ~4 Ga and, if so, how long it lasted. In addition, we would like to see if there are identifiable events in multiple samples from the H and LL parent bodies, equivalent to the well-known ~500 Ma event for L chon-drites. Finally, even within the well-studied L chondrites, we would like to search for further hints of the 800-900 Ma event that appears to be present within some of the meteorites [1], and compare meteorite with ages of roughly 500 Ma with the more detailed age for this event apparently given by Swedish fossil meteorites [6].

Hence, we are studying of shocked chondrites, combining petrological analyses with Ar-Ar dating. Petrological analyses are made to verify that the melts are produced by bulk melting host lithologies and determining the extent to which metallic, sulfide, and silicate-oxide components have been redistributed by shock. Silicate and metallic textures and compositions are used to determine the cooling rates of the melts, which can, in turn, help constrain the size of the impact cratering event [e.g., 1,2]. For each sample, we will perform Ar-Ar analysis on at least three samples each of impact melt and unmelted clasts, to use the dif-ferent thermal histories the different types of material have ex-perienced to try to maximize the amount of chronological infor-mation we can obtain about each meteorite [4].

Our current set of samples, which have been studied petro-graphically, have undergone neutron irradiation for Ar-Ar dating, and are being analyzed for Ar-Ar, includes the following: NWA 1701, an LL chondrite impact melt breccia whose Ar-Ar sys-tematics indicate an impact no more than ~2.8 Ga ago (younger than previously documented LL impacts); NWA 2058, an mete-orite of H chondrite composition that is more than 90% impact melt.; Gao-Guenie, and H with impact melt veins; LAP 02240, and H impact melt breccia; and NWA 2085, an L impact melt breccia whose chronology has not previously been studied. Addi-tional data will be presented at the meeting.

References: [1] Kring D. A. et al. (1996) Journal of Geo-physical. Research, 101, 29,353-29,371. [2] Kring D. A. et al. (1999) Meteoritics &. Planetary Science, 34, 663-669. [3] Kring D. A. et al. (2000) Lunar & Planetary Science XXXI, Abstract 1688. [4] Grier J. A. et al. (2004) Meteoritics & Planetary Sci-ence, 39, 1475-1493. [5] Bogard D. D. (1995) Meteoritics, 30, 244-268. [6] Schmitz B. et al. (2003) Science, 300, 961-964.


LUNAR IMPACT HISTORIES DEDUCED FROM Ar-Ar. T. D. Swindle1, D. A. Kring1, B. A. Cohen2, J. W. Delano3 and N. E. B. Zellner4. 1Lunar and Planetary Laboratory, U. of Ari-zona, Tucson AZ. E-mail: [email protected]. 2Institute of Meteoritics, U. of New Mexico, Albuquerque NM. 3University at Albany (SUNY), Albany NY. 4Albion College, Albion MI.

Four data sets have been produced from impact-generated lu-

nar materials in the last 15 years. These four data sets, all based on Ar-Ar dating, do not at first appear to be telling the same story, but may not be inconsistent with one another, because they all sample different material. To understand our current knowl-edge of the Moon’s impact history, one needs to compare these data sets with each other, and with other information available.

These data sets include (A) carefully selected impact melt rocks from different Apollo missions [1-3], (B) crystallized im-pact melt clasts from lunar meteorites, with chemical composi-tions suggesting origins far from the Near Side Apollo sites, [4-6], (C) impact glasses of unknown chemistry from Apollo 14 soil [7], and (D) impact glasses from Apollo 14, 16, and 17, selected for unusual (for their location) chemistry [8-10]. Sets (B) and (D) were obtained at Arizona. In addition, several groups continue to obtain ages on various other lunar samples. Many impact samples have “lunar cataclysm” ages of ~3.9 Ga. A few have older ages [11], though not enough to suggest a heavy bombardment earlier.

One question that has appeared is the meaning of younger ages (<3.8 Ga), which are common among crystallized impact melts and among impact glasses culled from the lunar soil. Each of the systematic data sets obtained has selected samples with specific criteria, testing specific ideas. The Apollo samples of (A) were expected to be Near Side basin samples, but the lunar mete-orite impact melts (B) were expected to come from large (though not necessarily basin-sized) impacts, perhaps distant from the Near Side, the glasses of (C) were selected randomly, and the glasses of (D) were selected to sample impacts with specific chemistries distinct from the landing sites. Neither set of glasses was selected with the cataclysm in mind. In fact, basin-sized im-pacts that define the cataclysm may not be effective at producing glass, which requires extremely rapid cooling (cold surround-ings).

Although the present sample sets have answered the first-order questions (~3.9 Ga impact ages are common, older ones rare), the second-order questions (how long was the cataclysm, how low was the impact rate before it) remain open, and will re-quire large data sets of well-characterized samples to properly address.

References: [1] Dalrymple G. B. and Ryder G. (1991) Geo-physical Research Letters, 18, 1163-1166. [2] Dalrymple G. B. and Ryder G. (1993) Journal of Geophysical Research, 98, 13,085-13,095. [3] Dalrymple G. B. and Ryder G. (1996) Journal of Geophysical Research, 101, 26,069-26,084. [4] Cohen B. A. et al. (2000) Science, 290, 1754-1756. [5] Cohen B. A. et al. (2005) Meteoritics and Planetary Science, 40, in press. [6] Cohen B. A. et al. (2005) 36th Lunar and Planetary Science, Abstract 1481. [7] Culler T. S. et al. (2000) Science, 287, 1785-1788. [8] Zellner N. E. B. et al. (2003) 34th Lunar and Planetary Science, Abstract 1157. [9] Zellner N. E. B. et al. (2005) 36th Lunar and Planetary Science, Abstract 1204. [10] Zellner N. E. B. et al. (2005) 36th Lunar and Planetary Science, Abstract 1199. [11] Bogard D. D. (2005) 36th Lunar and Planetary Science, Abstract 1131.



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